Methods for filtering air for a gas turbine system

ABSTRACT

Methods for cleaning air intake for a gas turbine system include utilizing filter arrangements that include a barrier media, usually pleated, treated with a deposit of fine fibers. The media is particularly advantageous in high operating temperature (140 to 350° f.) and/or high humidity (greater than 50 to 90% RH) environments.

RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. § 119(e) to U.S.provisional application Ser. No. 60/230,138, filed on Sep. 5, 2000,incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates to a filter arrangement andfiltration method. More specifically, it concerns an arrangement forfiltering particulate material from a gas flow stream, for example, anair stream. The invention also concerns a method for achieving thedesirable removal of particulate material from such a gas flow stream.

BACKGROUND OF THE INVENTION

[0003] The present invention is an on-going development of DonaldsonCompany Inc., of Minneapolis, Minn., the assignee of the presentinvention. The disclosure concerns continuing technology developmentrelated, in part, to the subjects characterized in U.S. Pat. Nos. B24,720,292; Des 416,308; 5,613,992; 4,020,783; and 5,112,372. Each of thepatents identified in the previous sentence is also owned by Donaldson,Inc., of Minneapolis, Minn.; and, the complete disclosure of each isincorporated herein by reference.

[0004] The invention also relates to polymer materials can bemanufactured with improved environmental stability to heat, humidity,reactive materials and mechanical stress. Such materials can be used inthe formation of fine fibers such as microfibers and nanofiber materialswith improved stability and strength. As the size of fiber is reducedthe survivability of the materials is increasingly more of a problem.Such fine fibers are useful in a variety of applications. In oneapplication, filter structures can be prepared using this fine fibertechnology. The invention relates to polymers, polymeric composition,fiber, filters, filter constructions, and methods of filtering.Applications of the invention particularly concern filtering ofparticles from fluid streams, for example from air streams and liquid(e.g. non-aqueous and aqueous) streams. The techniques described concernstructures having one or more layers of fine fibers in the filter media.The compositions and fiber sizes are selected for a combination ofproperties and survivability.

[0005] The invention relates to polymeric compositions with improvedproperties that can be used in a variety of applications including theformation of fibers, fine fiber, microfibers, nanofibers, fiber webs,fibrous mats, permeable structures such as membranes, coatings or films.The polymeric materials of the invention are compositions that havephysical properties that permit the polymeric material, in a variety ofphysical shapes or forms, to have resistance to the degradative effectsof humidity, heat, air flow, chemicals and mechanical stress or impact.In making non-woven filter media, a variety of materials have been usedincluding fiberglass, metal, ceramics and a wide range of polymericcompositions. A variety of techniques have been used for the manufactureof small diameter fine fiber such as micro- and nanofibers. One methodinvolves passing the material through a fine capillary or opening eitheras a melted material or in a solution that is subsequently evaporated.Fibers can also be formed by using “spinnerets” typical for themanufacture of synthetic fiber such as nylon. Electrostatic spinning isalso known. Such techniques involve the use of a hypodermic needle,nozzle, capillary or movable emitter. These structures provide liquidsolutions of the polymer that are then attracted to a collection zone bya high voltage electrostatic field. As the materials are pulled from theemitter and accelerate through the electrostatic zone, the fiber becomesvery thin and can be formed in a fiber structure by solvent evaporation.

[0006] As more demanding applications are envisioned for filtrationmedia, significantly improved materials are required to withstand therigors of high temperature 100° F. to 250° F. and up to 300° F., highhumidity 10% to 90% up to 100% RH, high flow rates of both gas andliquid, and filtering micron and submicron particulates (ranging fromabout 0.01 to over 10 microns) and removing both abrasive andnon-abrasive and reactive and non-reactive particulate from the fluidstream.

[0007] Accordingly, a substantial need exists for polymeric materials,micro- and nanofiber materials and filter structures that provideimproved properties for cleaning air intake into gas turbine systems athigher temperatures, higher humidities and high flow rates.

SUMMARY OF THE INVENTION

[0008] Herein, general methods for the cleaning of an air intake streamin a gas turbine system are provided. The methods include utilizingpreferred filter media. In general, the preferred media concernutilization, within an air filter, of barrier media, typically pleatedmedia, and fine fibers, to advantage.

[0009] The filter media includes at least a micro- or nanofiber weblayer in combination with a substrate material in a mechanically stablefilter structure. These layers together provide excellent filtering,high particle capture, efficiency at minimum flow restriction when afluid such as a gas or liquid passes through the filter media. Thesubstrate can be positioned in the fluid stream upstream, downstream orin an internal layer. A variety of industries have directed substantialattention in recent years to the use of filtration media for filtration,i.e. the removal of unwanted particles from a fluid such as gas orliquid. The common filtration process removes particulate from fluidsincluding an air stream or other gaseous stream or from a liquid streamsuch as a hydraulic fluid, lubricant oil, fuel, water stream or otherfluids. Such filtration processes require the mechanical strength,chemical and physical stability of the microfiber and the substratematerials. The filter media can be exposed to a broad range oftemperature conditions, humidity, mechanical vibration and shock andboth reactive and non-reactive, abrasive or non-abrasive particulatesentrained in the fluid flow. Further, the filtration media often requirethe self-cleaning ability of exposing the filter media to a reversepressure pulse (a short reversal of fluid flow to remove surface coatingof particulate) or other cleaning mechanism that can remove entrainedparticulate from the surface of the filter media. Such reverse cleaningcan result in substantially improved (i.e.) reduced pressure drop afterthe pulse cleaning. Particle capture efficiency typically is notimproved after pulse cleaning, however pulse cleaning will reducepressure drop, saving energy for filtration operation. Such filters canbe removed for service and cleaned in aqueous or non-aqueous cleaningcompositions. Such media are often manufactured by spinning fine fiberand then forming an interlocking web of microfiber on a poroussubstrate. In the spinning process the fiber can form physical bondsbetween fibers to interlock the fiber mat into a integrated layer. Sucha material can then be fabricated into the desired filter format such ascartridges, flat disks, canisters, panels, bags and pouches. Within suchstructures, the media can be substantially pleated, rolled or otherwisepositioned on support structures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 depicts a typical electrostatic emitter driven apparatusfor production of the fine fibers of the invention.

[0011]FIG. 2 shows the apparatus used to introduce fine fiber ontofilter substrate into the fine fiber forming technology shown in FIG. 1.

[0012]FIG. 3 is a depiction of the typical internal structure of asupport material and a separate depiction of the fine fiber material ofthe invention compared to small, i.e. 2 and 5 micron particulatematerials.

[0013]FIGS. 4 through 11 are analytical ESCA spectra relating to Example13.

[0014]FIG. 12 shows the stability of the 0.23 and 0.45 microfibermaterial of the invention from Example 5.

[0015]FIGS. 13 through 16 show the improved temperature and humiditystability of the materials of Examples 5 and 6 when compared tounmodified nylon copolymer solvent soluble polyamide.

[0016]FIGS. 17 through 20 demonstrate that the blend of two copolymers,a nylon homopolymer and a nylon copolymer, once heat treated andcombined with additives form a single component material that does notdisplay distinguishable characteristics of two separate polymermaterials, but appears to be a crosslinked or otherwise chemicallyjoined single phase.

[0017]FIG. 21 is a schematic cross-sectional view of a gas turbine airintake filtration system, utilized in the methods of this disclosure;and

[0018]FIG. 22 is a schematic cross-sectional view of another gas turbineintake filtration system, similar to the system of FIG. 21 but smaller,utilized in the methods of this disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The invention provides an improved polymeric material. Thispolymer has improved physical and chemical stability. The polymer finefiber (microfiber and nanofiber) can be fashioned into useful productformats. Nanofiber is a fiber with diameter less than 200 nanometer or0.2 micron. Microfiber is a fiber with diameter larger than 0.2 micron,but not larger than 10 microns. This fine fiber can be made in the formof an improved multi-layer microfiltration media structure. The finefiber layers of the invention comprise a random distribution of finefibers which can be bonded to form an interlocking net. Filtrationperformance is obtained largely as a result of the fine fiber barrier tothe passage of particulate. Structural properties of stiffness,strength, pleatability are provided by the substrate to which the finefiber adhered. The fine fiber interlocking networks have as importantcharacteristics, fine fibers in the form of microfibers or nanofibersand relatively small spaces between the fibers. Such spaces typicallyrange, between fibers, of about 0.01 to about 25 microns or often about0.1 to about 10 microns. The filter products comprising a fine fiberlayer and a cellulosic layer are thin with a choice of appropriatesubstrate. The fine fiber adds less than a micron in thickness to theoverall fine fiber plus substrate filter media. In service, the filterscan stop incident particulate from passing through the fine fiber layerand can attain substantial surface loadings of trapped particles. Theparticles comprising dust or other incident particulates rapidly form adust cake on the fine fiber surface and maintains high initial andoverall efficiency of particulate removal. Even with relatively finecontaminants having a particle size of about 0.01 to about 1 micron, thefilter media comprising the fine fiber has a very high dust capacity.

[0020] The polymer materials as disclosed herein have substantiallyimproved resistance to the undesirable effects of heat, humidity, highflow rates, reverse pulse cleaning, operational abrasion, submicronparticulates, cleaning of filters in use and other demanding conditions.The improved microfiber and nanofiber performance is a result of theimproved character of the polymeric materials forming the microfiber ornanofiber. Further, the filter media of the invention using the improvedpolymeric materials of the invention provides a number of advantageousfeatures including higher efficiency, lower flow restriction, highdurability (stress related or environmentally related) in the presenceof abrasive particulates and a smooth outer surface free of loose fibersor fibrils. The overall structure of the filter materials provides anoverall thinner media allowing improved media area per unit volume,reduced velocity through the media, improved media efficiency andreduced flow restrictions.

[0021] A preferred mode of the invention is a polymer blend comprising afirst polymer and a second, but different polymer (differing in polymertype, molecular weight or physical property) that is conditioned ortreated at elevated temperature. The polymer blend can be reacted andformed into a single chemical specie or can be physically combined intoa blended composition by an annealing process. Annealing implies aphysical change, like crystallinity, stress relaxation or orientation.Preferred materials are chemically reacted into a single polymericspecie such that a Differential Scanning Calorimeter analysis reveals asingle polymeric material. Such a material, when combined with apreferred additive material, can form a surface coating of the additiveon the microfiber that provides oleophobicity, hydrophobicity or otherassociated improved stability when contacted with high temperature, highhumidity and difficult operating conditions. The fine fiber of the classof materials can have a diameter of 2 microns to less than 0.01 micron.Such microfibers can have a smooth surface comprising a discrete layerof the additive material or an outer coating of the additive materialthat is partly solubilized or alloyed in the polymer surface, or both.Preferred materials for use in the blended polymeric systems includenylon 6; nylon 66; nylon 6-10; nylon (6-66-610) copolymers and otherlinear generally aliphatic nylon compositions. A preferred nyloncopolymer resin (SVP-651) was analyzed for molecular weight by the endgroup titration. (J. E. Walz and G. B. Taylor, determination of themolecular weight of nylon, Anal. Chem. Vol. 19, Number 7, pp 448-450(1947). A number average molecular weight (W_(n)) was between 21,500 and24,800. The composition was estimated by the phase diagram of melttemperature of three component nylon, nylon 6 about 45%, nylon 66 about20% and nylon 610 about 25%. (Page 286, Nylon Plastics Handbook, MelvinKohan ed. Hanser Publisher, New York (1995)).

[0022] Reported physical properties of SVP 651 resin are: Property ASTMMethod Units Typical Value Specific Gravity D-792 —  1.08 WaterAbsorption D-570 % 2.5 (24 hr immersion) Hardness D-240 Shore D 65Melting Point DSC ° C.(° F.) 154 (309) Tensile Strength D-638 MPa (kpsi)50 (7.3) @ Yield Elongation at Break D-638 % 350 Flexural Modulus D-790MPa (kpsi) 180 (26) Volume Resistivity D-257 ohm-cm 10¹²

[0023] A polyvinylalcohol having a hydrolysis degree of from 87 to99.9+% can be used in such polymer systems. These are preferably crosslinked. And they are most preferably crosslinked and combined withsubstantial quantities of the oleophobic and hydrophobic additivematerials.

[0024] Another preferred mode of the invention involves a singlepolymeric material combined with an additive composition to improvefiber lifetime or operational properties. The preferred polymers usefulin this aspect of the invention include nylon polymers, polyvinylidenechloride polymers, polyvinylidene fluoride polymers, polyvinylalcoholpolymers and, in particular, those listed materials when combined withstrongly oleophobic and hydrophobic additives that can result in amicrofiber or nanofiber with the additive materials formed in a coatingon the fine fiber surface. Again, blends of similar polymers such as ablend of similar nylons, similar polyvinylchloride polymers, blends ofpolyvinylidene chloride polymers are useful in this invention. Further,polymeric blends or alloys of differing polymers are also contemplatedby the invention. In this regard, compatible mixtures of polymers areuseful in forming the microfiber materials of the invention. Additivecomposition such a fluoro-surfactant, a nonionic surfactant, lowmolecular weight resins (e.g.) tertiary butylphenol resin having amolecular weight of less than about 3000 can be used. The resin ischaracterized by oligomeric bonding between phenol nuclei in the absenceof methylene bridging groups. The positions of the hydroxyl and thetertiary butyl group can be randomly positioned around the rings.Bonding between phenolic nuclei always occurs next to hydroxyl group,not randomly. Similarly, the polymeric material can be combined with analcohol soluble non-linear polymerized resin formed from bis-phenol A.Such material is similar to the tertiary butylphenol resin describedabove in that it is formed using oligomeric bonds that directly connectaromatic ring to aromatic ring in the absence of any bridging groupssuch as alkylene or methylene groups.

[0025] A particularly preferred material of the invention comprises amicrofiber material having a dimension of about 0.0001 to 5 microns. Themost preferred fiber size range between 0.001 to 0.2 micron. Such fiberswith the preferred size provide excellent filter activity, ease of backpulse cleaning and other aspects. The highly preferred polymer systemsof the invention have adhering characteristic such that when contactedwith a cellulosic substrate adheres to the substrate with sufficientstrength such that it is securely bonded to the substrate and can resistthe delaminating effects of a reverse pulse cleaning technique and othermechanical stresses. In such a mode, the polymer material must stayattached to the substrate while undergoing a pulse clean input that issubstantially equal to the typical filtration conditions except in areverse direction across the filter structure. Such adhesion can arisefrom solvent effects of fiber formation as the fiber is contacted withthe substrate or the post treatment of the fiber on the substrate withheat or pressure. However, polymer characteristics appear to play animportant role in determining adhesion, such as specific chemicalinteractions like hydrogen bonding, contact between polymer andsubstrate occurring above or below Tg, and the polymer formulationincluding additives. Polymers plasticized with solvent or steam at thetime of adhesion can have increased adhesion.

[0026] An important aspect of the invention is the utility of suchmicrofiber or nanofiber materials formed into a filter structure. Insuch a structure, the fine fiber materials of the invention are formedon and adhered to a filter substrate. Natural fiber and synthetic fibersubstrates, like spun bonded fabrics, non-woven fabrics of syntheticfiber and non-wovens made from the blends of cellulosics, synthetic andglass fibers, non-woven and woven glass fabrics, plastic screen likematerials both extruded and hole punched, UF and MF membranes of organicpolymers can be used. Sheet-like substrate or cellulosic non-woven webcan then be formed into a filter structure that is placed in a fluidstream including an air stream or liquid stream for the purpose ofremoving suspended or entrained particulate from that stream. The shapeand structure of the filter material is up to the design engineer. Oneimportant parameter of the filter elements after formation is itsresistance to the effects of heat, humidity or both. One aspect of thefilter media of the invention is a test of the ability of the filtermedia to survive immersion in warm water for a significant period oftime. The immersion test can provide valuable information regarding theability of the fine fiber to survive hot humid conditions and to survivethe cleaning of the filter element in aqueous solutions that can containsubstantial proportions of strong cleaning surfactants and strongalkalinity materials. Preferably, the fine fiber materials of theinvention can survive immersion in hot water while retaining at least50% of the fine fiber formed on the surface of the substrate. Retentionof at least 50% of the fine fiber can maintain substantial fiberefficiency without loss of filtration capacity or increased backpressure. Most preferably retaining at least 75%.

[0027] The fine fibers that comprise the micro- or nanofiber containinglayer of the invention can be fiber and can have a diameter of about0.001 to 5 microns, 0.001 to 2 microns, 0.05 to 0.5 micron, preferably0.01 to 0.2 micron. The thickness of the typical fine fiber filtrationlayer ranges from about 0.1 to 3 micron (about 1 to 100 times) the fiberdiameter with a basis weight ranging from about 0.01 to 240micrograms-cm⁻².

[0028] Fluid streams such as air and gas streams often carry particulatematerial therein. The removal of some or all of the particulate materialfrom the fluid stream is needed. For example, air intake streams to thecabins of motorized vehicles, air in computer disk drives, HVAC air,clean room ventilation and applications using filter bags, barrierfabrics, woven materials, air to engines for motorized vehicles, or topower generation equipment; gas streams directed to gas turbines; and,air streams to various combustion furnaces, often include particulatematerial therein. In the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, it is desirable to remove theparticulate material because particulate can cause substantial damage tothe internal workings to the various mechanisms involved. In otherinstances, production gases or off gases from industrial processes orengines may contain particulate material therein. Before such gases canbe, or should be, discharged through various downstream equipment to theatmosphere, it may be desirable to obtain a substantial removal ofparticulate material from those streams.

[0029] A general understanding of some of the basic principles andproblems of air filter design can be understood by consideration of thefollowing types of filter media: surface loading media; and, depthmedia. Each of these types of media has been well studied, and each hasbeen widely utilized. Certain principles relating to them are described,for example, in U.S. Pat. Nos. 5,082,476; 5,238,474; and 5,364,456. Thecomplete disclosures of these three patents are incorporated herein byreference.

[0030] The “lifetime” of a filter is typically defined according to aselected limiting pressure drop across the filter. The pressure buildupacross the filter defines the lifetime at a defined level for thatapplication or design. Since this buildup of pressure is a result ofload, for systems of equal efficiency a longer life is typicallydirectly associated with higher capacity. Efficiency is the propensityof the media to trap, rather than pass, particulates. It should beapparent that typically the more efficient a filter media is at removingparticulates from a gas flow stream, in general the more rapidly thefilter media will approach the “lifetime” pressure differential(assuming other variables to be held constant). In this application theterm “unchanged for filtration purposes” refers to maintainingsufficient efficiency to remove particulate from the fluid stream as isnecessary for the selected application.

[0031] Polymeric materials have been fabricated in non-woven and wovenfabrics, fibers and microfibers. The polymeric material provides thephysical properties required for product stability. These materialsshould not change significantly in dimension, suffer reduced molecularweight, become less flexible or subject to stress cracking or physicallydeteriorate in the presence of sunlight, humidity, high temperatures orother negative environmental effects. The invention relates to animproved polymeric material that can maintain physical properties in theface of incident electromagnetic radiation such as environmental light,heat, humidity and other physical challenges.

[0032] Polymer materials that can be used in the polymeric compositionsof the invention include both addition polymer and condensation polymermaterials such as polyolefin, polyacetal, polyamide, polyester,cellulose ether and ester, polyalkylene sulfide, polyarylene oxide,polysulfone, modified polysulfone polymers and mixtures thereof.Preferred materials that fall within these generic classes includepolyethylene, polypropylene, poly(vinylchloride), polymethylmethacrylate(and other acrylic resins), polystyrene, and copolymers thereof(including ABA type block copolymers), poly(vinylidene fluoride),poly(vinylidene chloride), polyvinylalcohol in various degrees ofhydrolysis (87% to 99.5%) in crosslinked and non-crosslinked forms.Preferred addition polymers tend to be glassy (a Tg greater than roomtemperature). This is the case for polyvinylchloride andpolymethylmethacrylate, polystyrene polymer compositions or alloys orlow in crystallinity for polyvinylidene fluoride and polyvinylalcoholmaterials. One class of polyamide condensation polymers are nylonmaterials. The term “nylon” is a generic name for all long chainsynthetic polyamides. Typically, nylon nomenclature includes a series ofnumbers such as in nylon-6,6 which indicates that the starting materialsare a C₆ diamine and a C₆ diacid (the first digit indicating a C₆diamine and the second digit indicating a C₆ dicarboxylic acidcompound). Another nylon can be made by the polycondensation of epsiloncaprolactam in the presence of a small amount of water. This reactionforms a nylon-6 (made from a cyclic lactam—also known asepisilon-aminocaproic acid) that is a linear polyamide. Further, nyloncopolymers are also contemplated. Copolymers can be made by combiningvarious diamine compounds, various diacid compounds and various cycliclactam structures in a reaction mixture and then forming the nylon withrandomly positioned monomeric materials in a polyamide structure. Forexample, a nylon 6,6-6,10 material is a nylon manufactured fromhexamethylene diamine and a C₆ and a C₁₀ blend of diacids. A nylon6-6,6-6,10 is a nylon manufactured by copolymerization ofepsilonaminocaproic acid, hexamethylene diamine and a blend of a C₆ anda C₁₀ diacid material.

[0033] Block copolymers are also useful in the process of thisinvention. With such copolymers the choice of solvent swelling agent isimportant. The selected solvent is such that both blocks were soluble inthe solvent. One example is a ABA (styrene-EP-styrene) or AB(styrene-EP) polymer in methylene chloride solvent. If one component isnot soluble in the solvent, it will form a gel. Examples of such blockcopolymers are Kraton® type of styrene-b-butadiene andstyrene-b-hydrogenated butadiene(ethylene propylene), Pebax® type ofe-caprolactam-b-ethylene oxide, Sympatex® polyester-b-ethylene oxide andpolyurethanes of ethylene oxide and isocyanates.

[0034] Addition polymers like polyvinylidene fluoride, syndiotacticpolystyrene, copolymer of vinylidene fluoride and hexafluoropropylene,polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers, suchas poly(acrylonitrile) and its copolymers with acrylic acid andmethacrylates, polystyrene, poly(vinyl chloride) and its variouscopolymers, poly(methyl methacrylate) and its various copolymers, can besolution spun with relative ease because they are soluble at lowpressures and temperatures. However, highly crystalline polymer likepolyethylene and polypropylene require high temperature, high pressuresolvent if they are to be solution spun. Therefore, solution spinning ofthe polyethylene and polypropylene is very difficult. Electrostaticsolution spinning is one method of making nanofibers and microfiber.

[0035] We have also found a substantial advantage to forming polymericcompositions comprising two or more polymeric materials in polymeradmixture, alloy format or in a crosslinked chemically bonded structure.We believe such polymer compositions improve physical properties bychanging polymer attributes such as improving polymer chain flexibilityor chain mobility, increasing overall molecular weight and providingreinforcement through the formation of networks of polymeric materials.

[0036] In one embodiment of this concept, two related polymer materialscan be blended for beneficial properties. For example, a high molecularweight polyvinylchloride can be blended with a low molecular weightpolyvinylchloride. Similarly, a high molecular weight nylon material canbe blended with a low molecular weight nylon material. Further,differing species of a general polymeric genus can be blended. Forexample, a high molecular weight styrene material can be blended with alow molecular weight, high impact polystyrene. A Nylon-6 material can beblended with a nylon copolymer such as a Nylon-6; 6,6; 6,10 copolymer.Further, a polyvinylalcohol having a low degree of hydrolysis such as a87% hydrolyzed polyvinylalcohol can be blended with a fully orsuperhydrolyzed polyvinylalcohol having a degree of hydrolysis between98 and 99.9% and higher. All of these materials in admixture can becrosslinked using appropriate crosslinking mechanisms. Nylons can becrosslinked using crosslinking agents that are reactive with thenitrogen atom in the amide linkage. Polyvinylalcohol materials can becrosslinked using hydroxyl reactive materials such as monoaldehydes,such as formaldehyde, ureas, melamine-formaldehyde resin and itsanalogues, boric acids and other inorganic compounds. dialdehydes,diacids, urethanes, epoxies and other known crosslinking agents.Crosslinking technology is a well known and understood phenomenon inwhich a crosslinking reagent reacts and forms covalent bonds betweenpolymer chains to substantially improve molecular weight, chemicalresistance, overall strength and resistance to mechanical degradation.

[0037] We have found that additive materials can significantly improvethe properties of the polymer materials in the form of a fine fiber. Theresistance to the effects of heat, humidity, impact, mechanical stressand other negative environmental effect can be substantially improved bythe presence of additive materials. We have found that while processingthe microfiber materials of the invention, that the additive materialscan improve the oleophobic character, the hydrophobic character and canappear to aid in improving the chemical stability of the materials. Webelieve that the fine fibers of the invention in the form of amicrofiber are improved by the presence of these oleophobic andhydrophobic additives as these additives form a protective layercoating, ablative surface or penetrate the surface to some depth toimprove the nature of the polymeric material. We believe the importantcharacteristics of these materials are the presence of a stronglyhydrophobic group that can preferably also have oleophobic character.Strongly hydrophobic groups include fluorocarbon groups, hydrophobichydrocarbon surfactants or blocks and substantially hydrocarbonoligomeric compositions. These materials are manufactured incompositions that have a portion of the molecule that tends to becompatible with the polymer material affording typically a physical bondor association with the polymer while the strongly hydrophobic oroleophobic group, as a result of the association of the additive withthe polymer, forms a protective surface layer that resides on thesurface or becomes alloyed with or mixed with the polymer surfacelayers. For 0.2-micron fiber with 10% additive level, the surfacethickness is calculated to be around 50 Å, if the additive has migratedtoward the surface. Migration is believed to occur due to theincompatible nature of the oleophobic or hydrophobic groups in the bulkmaterial. A 50 Å thickness appears to be reasonable thickness forprotective coating. For 0.05-micron diameter fiber, 50 Å thicknesscorresponds to 20% mass. For 2 microns thickness fiber, 50 Å thicknesscorresponds to 2% mass. Preferably the additive materials are used at anamount of about 2 to 25 wt. %. Oligomeric additives that can be used incombination with the polymer materials of the invention includeoligomers having a molecular weight of about 500 to about 5000,preferably about 500 to about 3000 including fluoro-chemicals, nonionicsurfactants and low molecular weight resins or oligomers. Fluoro-organicwetting agents useful in this invention are organic moleculesrepresented by the formula

R_(f)—G

[0038] wherein R_(f) is a fluoroaliphatic radical and G is a group whichcontains at least one hydrophilic group such as cationic, anionic,nonionic, or amphoteric groups. Nonionic materials are preferred. R_(f)is a fluorinated, monovalent, aliphatic organic radical containing atleast two carbon atoms. Preferably, it is a saturated perfluoroaliphaticmonovalent organic radical. However, hydrogen or chlorine atoms can bepresent as substituents on the skeletal chain. While radicals containinga large number of carbon atoms may function adequately, compoundscontaining not more than about 20 carbon atoms are preferred since largeradicals usually represent a less efficient utilization of fluorine thanis possible with shorter skeletal chains. Preferably, R_(f) containsabout 2 to 8 carbon atoms.

[0039] The cationic groups that are usable in the fluoro-organic agentsemployed in this invention may include an amine or a quaternary ammoniumcationic group which can be oxygen-free (e.g., —NH₂) oroxygen-containing (e.g., amine oxides). Such amine and quaternaryammonium cationic hydrophilic groups can have formulas such as —NH₂,—(NH₃)X, —(NH(R²)₂)X, —(NH(R²)₃)X, or —N(R₂)₂→O, where x is an anioniccounterion such as halide, hydroxide, sulfate, bisulfate, orcarboxylate, R² is H or C₁₋₁₈ alkyl group, and each R² can be the sameas or different from other R² groups. Preferably, R² is H or a C₁₋₁₆alkyl group and X is halide, hydroxide, or bisulfate.

[0040] The anionic groups which are usable in the fluoro-organic wettingagents employed in this invention include groups which by ionization canbecome radicals of anions. The anionic groups may have formulas such as—COOM, —SO₃M, —OSO₃M, —PO₃HM, —OPO₃M₂, or —OPO₃HM, where M is H, a metalion, (NR¹ ₄)⁺, or (SR¹ ₄)⁺, where each R¹ is independently H orsubstituted or unsubstituted C₁-C₆ alkyl. Preferably M is Na⁺ or K⁺. Thepreferred anionic groups of the fluoro-organo wetting agents used inthis invention have the formula —COOM or —SO₃M. Included within thegroup of anionic fluoro-organic wetting agents are anionic polymericmaterials typically manufactured from ethylenically unsaturatedcarboxylic mono- and diacid monomers having pendent fluorocarbon groupsappended thereto. Such materials include surfactants obtained from 3MCorporation known as FC-430 and FC-431.

[0041] The amphoteric groups which are usable in the fluoro-organicwetting agent employed in this invention include groups which contain atleast one cationic group as defined above and at least one anionic groupas defined above.

[0042] The nonionic groups which are usable in the fluoro-organicwetting agents employed in this invention include groups which arehydrophilic but which under pH conditions of normal agronomic use arenot ionized. The nonionic groups may have formulas such as —O(CH₂CH₂)xOHwhere x is greater than 1, —SO₂NH₂, —SO₂NHCH₂CH₂OH, —SO₂N(CH₂CH₂H)₂,—CONH₂, —CONHCH₂CH₂OH, or —CON(CH₂CH₂OH)₂. Examples of such materialsinclude materials of the following structure:

F(CF₂CF₂)_(n)—CH₂CH₂O—(CH₂CH₂O)_(m)—H

[0043] wherein n is 2 to 8 and m is 0 to 20.

[0044] Other fluoro-organic wetting agents include those cationicfluorochemicals described, for example in U.S. Pat. Nos. 2,764,602;2,764,603; 3,147,064 and 4,069,158. Such amphoteric fluoro-organicwetting agents include those amphoteric fluorochemicals described, forexample, in U.S. Pat. Nos. 2,764,602; 4,042,522; 4,069,158; 4,069,244;4,090,967; 4,161,590 and 4,161,602. Such anionic fluoro-organic wettingagents include those anionic fluorochemicals described, for example, inU.S. Pat. Nos. 2,803,656; 3,255,131; 3,450,755 and 4,090,967.

[0045] Examples of such materials are duPont Zonyl FSN and duPont ZonylFSO nonionic surfactants. Another aspect of additives that can be usedin the polymers of the invention include low molecular weightfluorocarbon acrylate materials such as 3M's Scotchgard material havingthe general structure:

CF₃(CX₂)_(n)-acrylate

[0046] wherein X is —F or —CF₃ and n is 1 to 7.

[0047] Further, nonionic hydrocarbon surfactants including lower alcoholethoxylates, fatty acid ethoxylates, nonylphenol ethoxylates, etc. canalso be used as additive materials for the invention. Examples of thesematerials include Triton X-100 and Triton N-101.

[0048] A useful material for use as an additive material in thecompositions of the invention are tertiary butylphenol oligomers. Suchmaterials tend to be relatively low molecular weight aromatic phenolicresins. Such resins are phenolic polymers prepared by enzymaticoxidative coupling. The absence of methylene bridges result in uniquechemical and physical stability. These phenolic resins can becrosslinked with various amines and epoxies and are compatible with avariety of polymer materials. These materials are generally exemplifiedby the following structural formulas which are characterized by phenolicmaterials in a repeating motif in the absence of methylene bridge groupshaving phenolic and aromatic groups.

[0049] wherein n is 2 to 20. Examples of these phenolic materialsinclude Enzo-BPA, Enzo-BPA/phenol, Enzo-TBP, Enzo-COP and other relatedphenolics were obtained from Enzymol International Inc., Columbus, Ohio.

[0050] It should be understood that an extremely wide variety of fibrousfilter media exist for different applications. The durable nanofibersand microfibers described in this invention can be added to any of themedia. The fibers described in this invention can also be used tosubstitute for fiber components of these existing media giving thesignificant advantage of improved performance (improved efficiencyand/or reduced pressure drop) due to their small diameter, whileexhibiting greater durability.

[0051] Polymer nanofibers and microfibers are known, however their usehas been very limited due to their fragility to mechanical stresses, andtheir susceptibility to chemical degradation due to their very highsurface area to volume ratio. The fibers described in this inventionaddress these limitations and will therefore be usable in a very widevariety of filtration, textile, membrane and other diverse applications.

DETAILED DESCRIPTION OF CERTAIN DRAWINGS

[0052] The microfiber or nanofiber of the unit can be formed by theelectrostatic spinning process. A suitable apparatus for forming thefiber is illustrated in FIG. 1. This apparatus includes a reservoir 80in which the fine fiber forming polymer solution is contained, a pump 81and a rotary type emitting device or emitter 40 to which the polymericsolution is pumped. The emitter 40 generally consists of a rotatingunion 41, a rotating portion 42 including a plurality of offset holes 44and a shaft 43 connecting the forward facing portion and the rotatingunion. The rotating union 41 provides for introduction of the polymersolution to the forward facing portion 42 through the hollow shaft 43.The holes 44 are spaced around the periphery of the forward facingportion 42. Alternatively, the rotating portion 42 can be immersed intoa reservoir of polymer fed by reservoir 80 and pump 81. The rotatingportion 42 then obtains polymer solution from the reservoir and as itrotates in the electrostatic field, a droplet of the solution isaccelerated by the electrostatic field toward the collecting media 70 asdiscussed below.

[0053] Facing the emitter 40, but spaced apart therefrom, is asubstantially planar grid 60 upon which the collecting media 70 (i.e.substrate or combined substrate is positioned. Air can be drawn throughthe grid. The collecting media 70 is passed around rollers 71 and 72which are positioned adjacent opposite ends of grid 60. A high voltageelectrostatic potential is maintained between emitter 40 and grid 60 bymeans of a suitable electrostatic voltage source 61 and connections 62and 63 which connect respectively to the grid 60 and emitter 40.

[0054] In use, the polymer solution is pumped to the rotating union 41or reservoir from reservoir 80. The forward facing portion 42 rotateswhile liquid exits from holes 44, or is picked up from a reservoir, andmoves from the outer edge of the emitter toward collecting media 70positioned on grid 60. Specifically, the electrostatic potential betweengrid 60 and the emitter 40 imparts a charge to the material which causeliquid to be emitted therefrom as thin fibers which are drawn towardgrid 60 where they arrive and are collected on substrate 12 or anefficiency layer 14. In the case of the polymer in solution, solvent isevaporated off the fibers during their flight to the grid 60; therefore,the fibers arrive at the substrate 12 or efficiency layer 14. The finefibers bond to the substrate fibers first encountered at the grid 60.Electrostatic field strength is selected to ensure that the polymermaterial as it is accelerated from the emitter to the collecting media70, the acceleration is sufficient to render the material into a verythin microfiber or nanofiber structure. Increasing or slowing theadvance rate of the collecting media can deposit more or less emittedfibers on the forming media, thereby allowing control of the thicknessof each layer deposited thereon. The rotating portion 42 can have avariety of beneficial positions. The rotating portion 42 can be placedin a plane of rotation such that the plane is perpendicular to thesurface of the collecting media 70 or positioned at any arbitrary angle.The rotating media can be positioned parallel to or slightly offset fromparallel orientation. FIG. 2 is a general schematic diagram of a processand apparatus for forming a layer of fine fiber on a sheet-likesubstrate or media. In FIG. 2, the sheet-like substrate is unwound atstation 20. The sheet-like substrate 20 a is then directed to a splicingstation 21 wherein multiple lengths of the substrate can be spliced forcontinuous operation. The continuous length of sheet-like substrate isdirected to a fine fiber technology station 22 comprising the spinningtechnology of FIG. 1 wherein a spinning device forms the fine fiber andlays the fine fiber in a filtering layer on the sheet-like substrate.After the fine fiber layer is formed on the sheet-like substrate in theformation zone 22, the fine fiber layer and substrate are directed to aheat treatment station 23 for appropriate processing. The sheet-likesubstrate and fine fiber layer is then tested in an efficiency monitor24 (see U.S. Pat. No. 5,203,201 which is expressly incorporated byreference herein for process and monitoring purposes) and nipped ifnecessary at a nip station 25. The sheet-like substrate and fiber layeris then steered to the appropriate winding station to be wound onto theappropriate spindle for further processing 26 and 27.

[0055]FIG. 3 is a scanning electromicrograph image showing therelationship of typical dust particles having a diameter of about 2 andabout 5 microns with respect to the sizes of pores in typical cellulosemedia and in the typical fine fiber structures. In FIG. 3A, the 2 micronparticle 31 and the 5 micron particle 32 is shown in a cellulosic media33 with pore sizes that are shown to be quite a bit larger than thetypical particle diameters. In sharp contrast, in FIG. 3B, the 2 micronparticle 31 appears to be approximately equal to or greater than thetypical openings between the fibers in the fiber web 35 while the 5micron particle 32 appears to be larger than any of the openings in thefine fiber web 35.

[0056] The foregoing general description of the various aspects of thepolymeric materials of the invention, the fine fiber materials of theinvention including both microfibers and nanofibers and the constructionof useful filter structures from the fine fiber materials of theinvention provides an understanding of the general technologicalprinciples of the operation of the invention. The following specificexemplary materials are examples of materials that can be used in theformation of the fine fiber materials of the invention and the followingmaterials disclose a best mode. The following exemplary materials weremanufactured with the following characteristics and process conditionsin mind. Electrospinning small diameter fiber less than 10 micron isobtained using an electrostatic force from a strong electric fieldacting as a pulling force to stretch a polymer jet into a very finefilament. A polymer melt can be used in the electrospinning process,however, fibers smaller than 1 micron are best made from polymersolution. As the polymer mass is drawn down to smaller diameter, solventevaporates and contributes to the reduction of fiber size. Choice ofsolvent is critical for several reasons. If solvent dries too quickly,then fibers tends to be flat and large in diameter. If the solvent driestoo slowly, solvent will redissolve the formed fibers. Thereforematching drying rate and fiber formation is critical. At high productionrates, large quantities of exhaust air flow helps to prevent a flammableatmosphere, and to reduce the risk of fire. A solvent that is notcombustible is helpful. In a production environment the processingequipment will require occasional cleaning. Safe low toxicity solventsminimize worker exposure to hazardous chemicals. Electrostatic spinningcan be done at a flow rate of 1.5 ml/min per emitter, a target distanceof 8 inches, an emitter voltage of 88 kV, an emitter rpm of 200 and arelative humidity of 45%.

[0057] The choice of polymer system is important for a givenapplication. For pulse cleaning application, an extremely thin layer ofmicrofiber can help to minimize pressure loss and provide an outersurface for particle capture and release. A thin layer of fibers of lessthan 2-micron diameter, preferably less than 0.3-micron diameter ispreferred. Good adhesion between microfiber or nanofiber and substratesupon which the microfibers or nanofibers are deposited is important.When filters are made of composites of substrate and thin layer ofmicro- and nanofibers, such composite makes an excellent filter mediumfor self-cleaning application. Cleaning the surface by back pulsingrepeatedly rejuvenates the filter medium. As a great force is exerted onthe surface, fine fiber with poor adhesion to substrates can delaminateupon a back pulse that passes from the interior of a filter through asubstrate to the micro fiber. Therefore, good cohesion between microfibers and adhesion between substrate fibers and electrospun fibers iscritical for successful use. Products that meet the above requirementscan be obtained using fibers made from different polymer materials.Small fibers with good adhesion properties can be made from suchpolymers like polyvinylidene chloride, poly vinyl alcohol and polymersand copolymers comprising various nylons such as nylon 6, nylon 4,6;nylon 6,6; nylon 6,10 and copolymers thereof. Excellent fibers can bemade from PVDF, but to make sufficiently small fiber diameters requireschlorinated solvents. Nylon 6, Nylon 66 and Nylon 6,10 can beelectrospun. But, solvents such as formic acid, m-cresol, tri-fluoroethanol, hexafluoro isopropanol are either difficult to handle or veryexpensive. Preferred solvents include water, ethanol, isopropanol,acetone and N-methylpyrrolidone due to their low toxicity. Polymerscompatible with such solvent systems have been extensively evaluated. Wehave found that fibers made from PVC, PVDC, polystyrene,polyacrylonitrile, PMMA, PVDF require additional adhesion means toattain structural properties. We also found that when polymers aredissolved in water, ethanol, isopropanol, acetone, methanol and mixturesthereof and successfully made into fibers, they have excellent adhesionto the substrate, thereby making an excellent filter medium forself-cleaning application. Self-cleaning via back air pulse or twist isuseful when filer medium is used for very high dust concentration.Fibers from alcohol soluble polyamides and poly(vinyl alcohol)s havebeen used successfully in such applications. Examples of alcohol solublepolyamides include Macromelt 6238, 6239, and 6900 from Henkel, Elvamide8061 and 8063 from duPont and SVP 637 and 651 from ShakespeareMonofilament Company. Another group of alcohol soluble polyamide is type8 nylon, alkoxy alkyl modifies nylon 66 (Ref. Page 447, Nylon Plasticshandbook, Melvin Kohan ed. Hanser Publisher, New York, 1995). Examplesof poly(vinyl alcohol) include PVA-217, 224 from Kuraray, Japan andVinol 540 from Air Products and Chemical Company. We have found thatfilters can be exposed to extremes in environmental conditions. Filtersin Saudi Arabian desert can be exposed to temperature as high as 150 F°or higher. Filters installed in Indonesia or Gulf Coast of US can beexposed high humidity above 90% RH and high temperature of 100 F°. Or,they can be exposed to rain. We have found that filters used under thehood of mobile equipment like cars, trucks, buses, tractors, andconstruction equipment can be exposed to high temperature (+200° F.),high relative humidity and other chemical environment. We have developedtest methods to evaluate survivability of microfiber systems under harshconditions. Soaking the filter media samples in hot water (140 F°) for 5minutes or exposure to high humidity, high temperature and air flow.

[0058] Single stage, self cleaning air filter systems are known. Onesuch system, commercially available, is the Donaldson GDX™ PulseCleaning Filter System available from Donaldson Company, Inc.,Minneapolis, Minn. In FIG. 21, a schematic, cross-sectional, depictionof a Donaldson GDX™ Pulse Cleaning Filter System 20 is presented. Thesystem of FIG. 21 is not prior art, in that it utilizes certainpreferred media formulations in its methods for filtering the air intakestream. Other than certain preferred media formulations utilized in thesystem of FIG. 21, the structure in the system of FIG. 21 is describedin U.S. Pat. No. 6,123,751, which is incorporated by reference herein,and which is commercially available from Donaldson.

[0059] Referring to FIG. 21, the system 220 includes a chamber 221having an air inlet side 222 and an air outlet side 223. Air enters thechamber 221 through a plurality of vertically spaced inlet hoods 226positioned along the air inlet side 222. The inlet hoods 226 function toprotect internal filters of the system 220 from the effects of rain,snow and sun. Also, the inlet hoods 226 are configured such that airentering the inlet hoods 226 is first directed in an upward directionindicated by arrow 227, and then deflected by deflector plates 228 in adownward direction indicated by arrow 229. The initial upward movementof air causes some particulate material and moisture from the air streamto settle or accumulate on lower regions 230 of the inlet hoods 226. Thesubsequent downward movement of air forces dust within the chamber 221downward toward a dust collection hopper 232 located at the bottom ofthe chamber 221.

[0060] The chamber 221 of the system 220 is divided into upstream anddownstream volumes 234 and 236 by a partition 238. The upstream volume234 generally represents the “dirty air section” of the air cleanersystem 220, while the downstream volume generally represents the “cleanair section” of the system 220. The partition 238 defines a plurality ofapertures 240 for allowing air to flow from the upstream volume 234 tothe downstream volume 236. Each aperture 240 is covered by an air filter242 or filter cartridge located in the upstream volume 234 of thechamber. The filters 242 are arranged and configured such that airflowing from the upstream volume 234 to the downstream volume 236 passesthrough the filters 242 prior to passing through the apertures 40.

[0061] For the particular filter arrangement shown, each air filter 242includes a pair of filter elements. For example, each air filter 242includes a cylindrical element 244 and, a somewhat truncated, conical,element 246. Each truncated, conical element 246 includes one end havinga major diameter and another end having aminor diameter. The cylindricalelement 244 and the truncated, conical element 246 of each filter 242are co-axially aligned and connected end-to-end with the minor diameterend of each conical element 246 being secured to one of the cylindricalelements 244 in a sealed manner. The major diameter end of eachtruncated, conical element 246 is secured to the partition 238 such thatan annular seal is formed around its corresponding aperture 240. Eachfilter 242 is generally co-axially aligned with respect to itscorresponding aperture 240 and has a longitudinal axis that is generallyhorizontal.

[0062] Each of the filter elements 242, 246 includes a media pack 260,262 forming a tubular construction 264, 266 and defining an open filterinterior 268, 270 within the construction. The open filter interior 268,270 is also a clean air plenum. Preferably, each media pack 260, 262 ispleated and comprises a composite of a substrate at least partiallycovered by a layer of fine fibers. Preferred formulations for mediacomposites are described below.

[0063] In general, during filtering, air is directed from the upstreamvolume 234 radially through the air filters 242 into interior volumes268, 270 (clean air plenums) of the filters 242. After being filtered,the air flows from the interior volumes 248 through the partition 238,via apertures 240, into the downstream clean air volume 236. The cleanair is then drawn out from the downstream volume 236, through apertures250, into a gas turbine intake, not shown.

[0064] Each aperture 240 of the partition 238 includes a pulse jet aircleaner 252 mounted in the downstream volume 236. Periodically, thepulse jet air cleaner 252 is operated to direct a pulse jet of air,shown at arrows 272, backwardly through the associated air filter 242,i.e. from the interior volume 268, 270 of the filter element outwardlyto shake or otherwise dislodge particular material trapped in or on thefilter media of the air filter 242. The pulse jet air cleaners 252 canbe sequentially operated from the top to the bottom of the chamber 221to eventually direct the dust particulate material blown from thefilters into the lower hopper 232, for removal.

[0065] Arrangements such as those shown in FIG. 21 may be rather large.Filter pairs used in such arrangements commonly include cylindricalfilters that are about 26 inches long and about 12.75 inches indiameter, and truncated conical filters that are about 26 inches long,about 12.75 inches in minor diameter, and about 17.5 inches in majordiameter. Such arrangements might be used, for example, for filteringintake air to a gas turbine system having an air flow demand on theorder of 8000 to 1.2 million cubic feet per minute (cfin).

[0066] In FIG. 22, another air intake filtration system for a gasturbine is illustrated. Other than preferred media formulations, thesystem shown in FIG. 22 is commercially available as the Donaldson GDX™Self-Cleaning Air Filter available from Donaldson Company. In FIG. 22, aschematic, cross-sectional, depiction of a Donaldson GDX™ Self CleaningAir Filter 120 is presented. The system of FIG. 22 is not prior art, inthat it utilizes certain preferred media formulations in its methods forfiltering the air intake stream. The system 120 of FIG. 22 is similar tothe system 20 of FIG. 21, except that the system 120 is depicted as asmaller, more compact unit.

[0067] In FIG. 22, the system 120 includes a chamber 121 having an airinlet side 122 and an air outlet side 123. Air enters the chamber 121through an inlet hood 126 positioned along the air inlet side 122. Theinlet hood 126 helps to direct air entering the inlet hood 126 in anupward direction indicated by arrow 127, and then deflect by deflectorplate 128 in a downward direction indicated by arrow 129. The downwardmovement of air forces dust within the chamber 21 downward toward a dustcollection hopper 132 located at the bottom of the chamber 121.

[0068] As with system 10 of FIG. 21, the chamber 121 of the system 120is divided into upstream and downstream volumes 134 and 136 by apartition 138. The upstream volume 134 represents the “dirty airsection” of the air cleaner system 120, while the downstream volumegenerally represents the “clean air section” of the system 120. Thepartition 138 defines a plurality of apertures 140 for allowing air toflow from the upstream volume 134 to the downstream volume 136. Eachaperture 140 is covered by an air filter 142 or filter cartridge locatedin the upstream volume 134 of the chamber. The filters 142 are arrangedand configured such that air flowing from the upstream volume 134 to thedownstream volume 136 passes through the filters 142 prior to passingthrough the apertures 140.

[0069] Each air filter 142 includes a pair of filter elements. Forexample, each air filter 142 includes a cylindrical element 144 and, atruncated, conical, element 146. Each truncated, conical element 146includes one end having a major diameter and another end having a minordiameter. The cylindrical element 144 and the truncated, conical element146 of each filter 142 are co-axially aligned and connected end-to-endwith the minor diameter end of each conical element 146 being secured toone of the cylindrical elements 144 in a sealed manner. The majordiameter end of each truncated, conical element 146 is secured to thepartition 138 such that an annular seal is formed around itscorresponding aperture 140. Each filter 142 is generally co-axiallyaligned with respect to its corresponding aperture 140 and has alongitudinal axis that is generally horizontal.

[0070] Each of the filter elements 144, 146 includes a media pack 160,162 forming a tubular construction 164, 166 and defining an open filterinterior 168, 170 within the construction. Preferably, each media pack160, 162 is pleated and comprises a composite of a substrate at leastpartially covered by a layer of fine fibers. Preferred formulations formedia composites are described below.

[0071] In general, during filtering, air is directed from the upstreamvolume 134 radially through the air filters 142 into interior volumes168, 170 (clean air plenums) of the filters 142. After being filtered,the air flows from the interior volumes 168, 170 through the partition138, via apertures 140, into the downstream clean air volume 136. Theclean air is then drawn out from the downstream volume 136, throughapertures 150, into a gas turbine intake, not shown.

[0072] Each aperture 140 of the partition 138 includes a pulse jet aircleaner 152 mounted in the downstream volume 136. Periodically, thepulse jet air cleaner 152 is operated to direct a pulse jet of airbackwardly, shown at arrows 172, through the associated air filter 142,i.e. from the interior volume 168, 170 of the filter element outwardlyto shake or otherwise dislodge particular material trapped in or on thefilter media of the air filter 142. The pulse jet air cleaners 152 canbe sequentially operated from the top to the bottom of the chamber 121to eventually direct the dust particulate material blown from thefilters into the lower hopper 132, for removal.

Preferred Media Formulations

[0073] In gas turbine air intake systems, during operation, the ambienttemperature or equipment operating temperature can sometimes reach atleast 140° F., and often is in the range of 150-350° F. Further, thehumidity can sometimes be high, in the range of at least 75% RH, often85 to 99+% RH. The temperature and/or humidity may adversely affect theoperating efficiency of the filter element. Constructing the filtermedia 260, 262 in the form of a composite of a barrier media treatedwith preferred formulations of fine fiber can improve the performance ofthe filter elements over prior art filter elements that are notconstructed from such media composites.

[0074] A fine fiber filter structure includes a bi-layer or multi-layerstructure wherein the filter contains one or more fine fiber layerscombined with or separated by one or more synthetic, cellulosic orblended webs. Another preferred motif is a structure including finefiber in a matrix or blend of other fibers.

[0075] We believe important characteristics of the fiber and microfiberlayers in the filter structure relate to temperature resistance,humidity or moisture resistance and solvent resistance, particularlywhen the microfiber is contacted with humidity, moisture or a solvent atelevated temperatures. Further, a second important property of thematerials of the invention relates to the adhesion of the material to asubstrate structure. The microfiber layer adhesion is an importantcharacteristic of the filter material such that the material can bemanufactured without delaminating the microfiber layer from thesubstrate, the microfiber layer plus substrate can be processed into afilter structure including pleats, rolled materials and other structureswithout significant delamination. We have found that the heating step ofthe manufacturing process wherein the temperature is raised to atemperature at or near but just below melt temperature of one polymermaterial, typically lower than the lowest melt temperature substantiallyimproves the adhesion of the fibers to each other and the substrate. Ator above the melt temperature, the fine fiber can lose its fibrousstructure. It is also critical to control heating rate. If the fiber isexposed to its crystallization temperature for extended period of time,it is also possible to lose fibrous structure. Careful heat treatmentalso improved polymer properties that result from the formation of theexterior additive layers as additive materials migrate to the surfaceand expose hydrophobic or oleophobic groups on the fiber surface.

[0076] While the temperature of the filter, under normal operatingcharacteristics is the same as the temperature of the ambient airpassing through the filter, the filter can be exposed to hightemperature. The filter can be exposed to high heat during time ofrestricted air flow, time when the operations stop and the equipmenttemperature is hot or in time of abnormal operation. The criteria forperformance is that the material be capable of surviving intact variousoperating filter temperatures, i.e. a temperature of 140° F., 160° F.,270° F., 300° F. for a period of time of 1 hour or 3 hours, depending onend use, while retaining 30%, 50%, 80% or 90% of filter efficiency. Analternative criteria for performances that the material is capable ofsurviving intact at various operating filter temperatures, i.e.temperatures of 140° F., 160° F., 270° F., 300° F., for a period of timeof 1 hours or 3 hours depending on end use, while retaining, dependingon end use, 30%, 50%, 80% or 90% of effective fine fibers in a filterlayer. Survival at these temperatures is important at low humidity, highhumidity, and in water saturated air. The microfiber and filter materialof the invention are deemed moisture resistant where the material cansurvive immersion at a temperature of greater than 160° F. whilemaintaining efficiency for a time greater than about 5 minutes.Similarly, solvent resistance in the microfiber material and the filtermaterial of the invention is obtained from a material that can survivecontact with a solvent such as ethanol, a hydrocarbon, a hydraulicfluid, or an aromatic solvent for a period of time greater than about 5minutes at 70° F. while maintaining 50% efficiency.

[0077] The fine fiber materials of the invention can be used in avariety of filter applications including pulse clean and non-pulsecleaned filters for dust collection, gas turbines and engine air intakeor induction systems; gas turbine intake or induction systems, heavyduty engine intake or induction systems, light vehicle engine intake orinduction systems; Zee filter; vehicle cabin air; off road vehicle cabinair, disk drive air, photocopier-toner removal; HVAC filters in bothcommercial or residential filtration applications.

[0078] Paper filter elements are widely used forms of surface loadingmedia. In general, paper elements comprise dense mats of cellulose,synthetic or other fibers oriented across a gas stream carryingparticulate material. The paper is generally constructed to be permeableto the gas flow, and to also have a sufficiently fine pore size andappropriate porosity to inhibit the passage of particles greater than aselected size therethrough. As the gases (fluids) pass through thefilter paper, the upstream side of the filter paper operates throughdiffusion and interception to capture and retain selected sizedparticles from the gas (fluid) stream. The particles are collected as adust cake on the upstream side of the filter paper. In time, the dustcake also begins to operate as a filter, increasing efficiency. This issometimes referred to as “seasoning,” i.e. development of an efficiencygreater than initial efficiency.

[0079] A simple filter design such as that described above is subject toat least two types of problems. First, a relatively simple flaw, i.e.rupture of the paper, results in failure of the system. Secondly,particulate material rapidly builds up on the upstream side of thefilter, as a thin dust cake or layer, increasing the pressure drop.Various methods have been applied to increase the “lifetime” ofsurface-loaded filter systems, such as paper filters. One method is toprovide the media in a pleated construction, so that the surface area ofmedia encountered by the gas flow stream is increased relative to aflat, non-pleated construction. While this increases filter lifetime, itis still substantially limited. For this reason, surface loaded mediahas primarily found use in applications wherein relatively lowvelocities through the filter media are involved, generally not higherthan about 20-30 feet per minute and typically on the order of about 10feet per minute or less. The term “velocity” in this context is theaverage velocity through the media (i.e. flow volume per media area).

[0080] In general, as air flow velocity is increased through a pleatedpaper media, filter life is decreased by a factor proportional to thesquare of the velocity. Thus, when a pleated paper, surface loaded,filter system is used as a particulate filter for a system that requiressubstantial flows of air, a relatively large surface area for the filtermedia is needed. For example, a typical cylindrical pleated paper filterelement of an over-the-highway diesel truck will be about 9-15 inches indiameter and about 12-24 inches long, with pleats about 1-2 inches deep.Thus, the filtering surface area of media (one side) is typically 30 to300 square feet.

[0081] In many applications, especially those involving relatively highflow rates, an alternative type of filter media, sometimes generallyreferred to as “depth” media, is used. A typical depth media comprises arelatively thick tangle of fibrous material. Depth media is generallydefined in terms of its porosity, density or percent solids content. Forexample, a 2-3% solidity media would be a depth media mat of fibersarranged such that approximately 2-3% of the overall volume comprisesfibrous materials (solids), the remainder being air or gas space.

[0082] Another useful parameter for defining depth media is fiberdiameter. If percent solidity is held constant, but fiber diameter(size) is reduced, pore size or interfiber space is reduced; i.e. thefilter becomes more efficient and will more effectively trap smallerparticles.

[0083] A typical conventional depth media filter is a deep, relativelyconstant (or uniform) density, media, i.e. a system in which thesolidity of the depth media remains substantially constant throughoutits thickness. By “substantially constant” in this context, it is meantthat only relatively minor fluctuations in density, if any, are foundthroughout the depth of the media. Such fluctuations, for example, mayresult from a slight compression of an outer engaged surface, by acontainer in which the filter media is positioned.

[0084] Gradient density depth media arrangements have been developed.some such arrangements are described, for example, in U.S. Pat. Nos.4,082,476; 5,238,474; and 5,364,456. In general, a depth mediaarrangement can be designed to provide “loading” of particulatematerials substantially throughout its volume or depth. Thus, sucharrangements can be designed to load with a higher amount of particulatematerial, relative to surface loaded systems, when full filter lifetimeis reached. However, in general the tradeoff for such arrangements hasbeen efficiency, since, for substantial loading, a relatively lowsolidity media is desired. Gradient density systems such as those in thepatents referred to above, have been designed to provide for substantialefficiency and longer life. In some instances, surface loading media isutilized as a “polish” filter in such arrangements.

[0085] A filter media construction according to the present inventionincludes a first layer of permeable coarse fibrous media or substratehaving a first surface. A first layer of fine fiber media is secured tothe first surface of the first layer of permeable coarse fibrous media.Preferably the first layer of permeable coarse fibrous materialcomprises fibers having an average diameter of at least 10 microns,typically and preferably about 12 (or 14) to 30 microns. Also preferablythe first layer of permeable coarse fibrous material comprises a mediahaving a basis weight of no greater than about 200 grams/meter²,preferably about 0.50 to 150 g/m², and most preferably at least 8 g/m².Preferably the first layer of permeable coarse fibrous media is at least0.0005 inch (12 microns) thick, and typically and preferably is about0.001 to 0.030 inch (25-800 microns) thick.

[0086] In preferred arrangements, the first layer of permeable coarsefibrous material comprises a material which, if evaluated separatelyfrom a remainder of the construction by the Frazier permeability test,would exhibit a permeability of at least 1 meter(s)/min, and typicallyand preferably about 2-900 meters/min. Herein when reference is made toefficiency, unless otherwise specified, reference is meant to efficiencywhen measured according to ASTM-1215-89, with 0.78μ monodispersepolystyrene spherical particles, at 20 fpm (6.1 meters/min) as describedherein.

[0087] Preferably the layer of fine fiber material secured to the firstsurface of the layer of permeable coarse fibrous media is a layer ofnano- and microfiber media wherein the fibers have average fiberdiameters of no greater than about 2 microns, generally and preferablyno greater than about 1 micron, and typically and preferably have fiberdiameters smaller than 0.5 micron and within the range of about 0.05 to0.5 micron. Also, preferably the first layer of fine fiber materialsecured to the first surface of the first layer of permeable coarsefibrous material has an overall thickness that is no greater than about30 microns, more preferably no more than 20 microns, most preferably nogreater than about 10 microns, and typically and preferably that iswithin a thickness of about 1-8 times (and more preferably no more than5 times) the fine fiber average diameter of the layer.

[0088] Certain preferred arrangements according to the present inventioninclude filter media as generally defined, in an overall filterconstruction. Some preferred arrangements for such use comprise themedia arranged in a cylindrical, pleated configuration with the pleatsextending generally longitudinally, i.e. in the same direction as alongitudinal axis of the cylindrical pattern. For such arrangements, themedia may be imbedded in end caps, as with conventional filters. Sucharrangements may include upstream liners and downstream liners ifdesired, for typical conventional purposes.

[0089] In some applications, media according to the present inventionmay be used in conjunction with other types of media, for exampleconventional media, to improve overall filtering performance orlifetime. For example, media according to the present invention may belaminated to conventional media, be utilized in stack arrangements; orbe incorporated (an integral feature) into media structures includingone or more regions of conventional media. It may be used upstream ofsuch media, for good load; and/or, it may be used downstream fromconventional media, as a high efficiency polishing filter.

[0090] Certain arrangements according to the present invention may alsobe utilized in liquid filter systems, i.e. wherein the particulatematerial to be filtered is carried in a liquid. Also, certainarrangements according to the present invention may be used in mistcollectors, for example arrangements for filtering fine mists from air.

[0091] According to the present invention, methods are provided forfiltering. The methods generally involve utilization of media asdescribed to advantage, for filtering. As will be seen from thedescriptions and examples below, media according to the presentinvention can be specifically configured and constructed to providerelatively long life in relatively efficient systems, to advantage.

[0092] Various filter designs are shown in patents disclosing andclaiming various aspects of filter structure and structures used withthe filter materials. Engel et al., U.S. Pat. No. 4,720,292, disclose aradial seal design for a filter assembly having a generally cylindricalfilter element design, the filter element being sealed by a relativelysoft, rubber-like end cap having a cylindrical, radially inwardly facingsurface. Kahlbaugh et al., U.S. Pat. No. 5,082,476, disclose a filterdesign using a depth media comprising a foam substrate with pleatedcomponents combined with the microfiber materials of the invention.Stifelman et al., U.S. Pat. No. 5,104,537, relate to a filter structureuseful for filtering liquid media. Liquid is entrained into the filterhousing, passes through the exterior of the filter into an interiorannular core and then returns to active use in the structure. Suchfilters are highly useful for filtering hydraulic fluids. Engel et al.,U.S. Pat. No. 5,613,992, show a typical diesel engine air intake filterstructure. The structure obtains air from the external aspect of thehousing that may or may not contain entrained moisture. The air passesthrough the filter while the moisture can pass to the bottom of thehousing and can drain from the housing. Gillingham et al., U.S. Pat. No.5,820,646, disclose a Z filter structure that uses a specific pleatedfilter design involving plugged passages that require a fluid stream topass through at least one layer of filter media in a “Z” shaped path toobtain proper filtering performance. The filter media formed into thepleated Z shaped format can contain the fine fiber media of theinvention. Glen et al., U.S. Pat. No. 5,853,442, disclose a bag housestructure having filter elements that can contain the fine fiberstructures of the invention. Berkhoel et al., U.S. Pat. No. 5,954,849,show a dust collector structure useful in processing typically airhaving large dust loads to filter dust from an air stream afterprocessing a workpiece generates a significant dust load in anenvironmental air. Lastly, Gillingham, U.S. Design Pat. No. 425,189,discloses a panel filter using the Z filter design.

EXPERIMENTAL

[0093] The following materials were produced using the followingelectrospin process conditions.

[0094] The following materials were spun using either a rotating emittersystem or a capillary needle system. Both were found to producesubstantially the same fibrous materials.

[0095] The flow rate was 1.5 mil/min per emitter, a target distance of 8inches, an emitter voltage of 88 kV, a relative humidity of 45%, and forthe rotating emitter an rpm of 35.

Example 1 Effect of Fiber Size

[0096] Fine fiber samples were prepared from a copolymer of nylon 6, 66,610 nylon copolymer resin (SVP-651) was analyzed for molecular weight bythe end group titration. (J. E. Walz and G. B. Taylor, determination ofthe molecular weight of nylon, Anal. Chem. Vol. 19, Number 7, pp 448450(1947). Number average molecular weight was between 21,500 and 24,800.The composition was estimated by the phase diagram of melt temperatureof three component nylon, nylon 6 about 45%, nylon 66 about 20% andnylon 610 about 25%. (Page 286, Nylon Plastics Handbook, Melvin Kohaned. Hanser Publisher, New York (1995)). Reported physical properties ofSVP 651 resin are: Property ASTM Method Units Typical Value SpecificGravity D-792 — 1.08 Water Absorption D-570 % 2.5 (24 hr immersion)Hardness D-240 Shore D 65 Melting Point DSC ° C.(° F.) 154 (309) TensileStrength D-638 MPa (kpsi) 50 (7.3) @ Yield Elongation at Break D-638 %350 Flexural Modulus D-790 MPa (kpsi) 180 (26) Volume Resistivity D-257ohm-cm 10¹²

[0097] to produce fiber of 0.23 and 0.45 micron in diameter. Sampleswere soaked in room temperature water, air-dried and its efficiency wasmeasured. Bigger fiber takes longer time to degrade and the level ofdegradation was less as can be seen in the plot of FIG. 12. Whilewishing not to be limited by certain theory, it appears that smallerfibers with a higher surface/volume ratio are more susceptible todegradation due to environmental effects. However, bigger fibers do notmake as efficient filter medium.

Example 2 Cross-Linking of Nylon Fibers with Phenolic Resin and EpoxyResin

[0098] In order to improve chemical resistance of fibers, chemicalcross-linking of nylon fibers was attempted. Copolyamide (nylon 6, 66,610) described earlier is mixed with phenolic resin, identified asGeorgia Pacific 5137 and spun into fiber. Nylon:Phenolic Resin ratio andits melt temperature of blends are shown here; Composition MeltingTemperature (° F.) Polyamide:Phenolic = 100:0 150 Polyamide:Phenolic =80:20 110 Polyamide:Phenolic = 65:35 94 Polyamide:Phenolic = 50:50 65

[0099] We were able to produce comparable fiber from the blends. The50:50 blend could not be cross-linked via heat as the fibrous structurewas destroyed. Heating 65:35 blend below 90 degree C. for 12 hoursimproves the chemical resistance of the resultant fibers to resistdissolution in alcohol. Blends of polyamide with epoxy resin, such Epon828 from Shell and Epi-Rez 510 can be used.

Example 3 Surface Modification though Fluoro Additive (Scotchgard®)Repellant

[0100] Alcohol miscible Scotchgard® FC-430 and 431 from 3M Company wereadded to polyamide before spinning. Add-on amount was 10% of solids.Addition of Scotchgard did not hinder fiber formation. THC bench showsthat Scotchgard-like high molecular weight repellant finish did notimprove water resistance. Scotchgard added samples were heated at 300 F°for 10 minutes as suggested by manufacturer.

Example 4 Modification with Coupling Agents

[0101] Polymeric films were cast from polyamides with tinanate couplingagents from Kenrich Petrochemicals, Inc. They include isopropyltriisostearoyl titanate (KR TTS), neopentyl (diallyl) oxytri (dioctyl)phosphato titanate (LICA12), neopentyl (dially) oxy, tri (N-ethylenediamino) ethyl zirconate (NZ44). Cast films were soaked in boilingwater. Control sample without coupling agent loses its strengthimmediately, while coupling agent added samples maintained its form forup to ten minutes. These coupling agents added samples were spun intofiber (0.2 micron fiber).

Example 5 Modification with Low Molecular Weight P-Tert-Butyl PhenolPolymer

[0102] Oligomers of para-tert-butyl phenol, molecular weight range 400to 1100, was purchased from Enzymol International, Columbus, Ohio. Theselow molecular weight polymers are soluble in low alcohols, such asethanol, isopropanol and butanol. These polymers were added toco-polyamide described earlier and electrospun into 0.2 micron fiberswithout adverse consequences. Some polymers and additives hinder theelectrospinning process. Unlike the conventional phenolic resindescribed in Example 2, we have found that this group of polymers doesnot interfere with fiber forming process.

[0103] We have found that this group of additive protects fine fibersfrom wet environment as see in the plot. FIGS. 13-16 show that oligomersprovide a very good protection at 140 F°, 100% humidity and theperformance is not very good at 160 F°. We have added this additivebetween 5% and 15% of polymer used. We have found that they are equallyeffective protecting fibers from exposure to high humidity at 140 F°. Wehave also found out that performance is enhanced when the fibers aresubjected to 150 C° for short period of time.

[0104] Table 1 shows the effect of temperature and time exposure of 10%add-on to polyamide fibers. TABLE 1 Efficiency Retained (%) After 140deg. F. Soak: Heating Time Temperature 1 min 3 min 10 min 150° C. 98.998.8 98.5 98.8 98.9 98.8 130° C. 95.4 98.7 99.8 96.7 98.6 99.6 110° C.82.8 90.5 91.7 86.2 90.9 85.7

[0105] This was a surprising result. We saw dramatic improvement inwater resistance with this family of additives. In order to understandhow this group of additive works, we have analyzed the fine fiber matwith surface analysis techniques called ESCA. 10% add-on samples shownin Table 1 were analyzed with ESCA at the University of Minnesota withthe results shown in Table 2. TABLE 2 Surface Composition(Polymer:Additive Ratio) Heating Time Temperature 1 min 3 min 10 min150° C. 40:60 40:60 50:50 130° C. 60:40 56:44 62:82 110° C. 63:37 64:3659:41 No Heat 77:23

[0106] Initially, it did not seem to make sense to find surfaceconcentration of additive more than twice of bulk concentration.However, we believe that this can be explained by the molecular weightof the additives. Molecular weight of the additive of about 600 is muchsmaller than that of host fiber forming polymer. As they are smaller insize, they can move along evaporating solvent molecules. Thus, weachieve higher surface concentration of additives. Further treatmentincreases the surface concentration of the protective additive. However,at 10 min exposure, 150 C°, did not increase concentration. This may bean indication that mixing of two components of copolyamide and oligomermolecules is happening as long chain polymer has a time to move around.What this analysis has taught us is that proper selection of posttreatment time and temperature can enhance performance, while too longexposure could have a negative influence.

[0107] We further examined the surface of these additive ladenmicrofibers using techniques called Time of Flight SIMS. This techniqueinvolves bombarding the subject with electrons and observes what iscoming from the surface. The samples without additives show organicnitrogen species are coming off upon bombardment with electron. This isan indication that polyamide species are broken off. It also showspresence of small quantity of impurities, such as sodium and silicone.Samples with additive without heat treatment (23% additive concentrationon surface) show a dominant species of t-butyl fragment, and small butunambiguous peaks observed peaks observed for the polyamides. Alsoobserved are high mass peaks with mass differences of 148 amu,corresponding to t-butyl phenol. For the sample treated at 10 min at 150C° (50% surface additive concentration by ESCA analysis), inspectionshows dominance of t-butyl fragments and trace, if at all, of peaks forpolyamide. It does not show peaks associated with whole t-butyl phenoland its polymers. It also shows a peak associated with C₂H₃O fragments.

[0108] The ToF SIMS analysis shows us that bare polyamide fibers willgive off broken nitrogen fragment from exposed polymer chain andcontaminants on the surface with ion bombardment. Additive without heattreatment shows incomplete coverage, indicating that additives do notcover portions of surface. The t-butyl oligomers are loosely organizedon the surface. When ion beam hits the surface, whole molecules can comeoff along with labile t-butyl fragment. Additive with heat treatmentpromotes complete coverage on the surface. In addition, the moleculesare tightly arranged so that only labile fragments such as t-butyl-, andpossibly CH═CH—OH, are coming off and the whole molecules of t-butylphenol are not coming off. ESCA and ToF SIMS look at different depths ofsurface. ESCA looks at deeper surface up to 100 Angstrom while ToF SIMSonly looks at 10-Angstrom depth. These analyses agree.

Example 6 Development of Surface Coated Interpolymer

[0109] Type 8 Nylon was originally developed to prepare soluble andcrosslinkable resin for coating and adhesive application. This type ofpolymer is made by the reaction of polyamide 66 with formaldehyde andalcohol in the presence of acid. (Ref. Cairns, T. L.; Foster, H. D.;Larcher, A. W.; Schneider, A. K.; Schreiber, R. S. J. Am. Chem. Soc.1949, 71, 651). This type of polymer can be elecrospun and can becross-linked. However, formation of fiber from this polymer is inferiorto copolyamides and crosslinking can be tricky.

[0110] In order to prepare type 8 nylon, 10-gallon high-pressure reactorwas charged with the following ratio: Nylon 66 (duPont Zytel 101)   10pounds Methanol 15.1 pounds Water  2.0 pounds Formaldehyde 12.0 pounds

[0111] The reactor is then flushed with nitrogen and is heated to atleast 135 C°. under pressure. When the desired temperature was reached,small quantity of acid was added as catalyst. Acidic catalysts includetrifluoroacetic acid, formic acid, toluene sulfonic acid, maleic acid,maleic anhydride, phthalic acid, phthalic anhydride, phosphoric acid,citric acid and mixtures thereof. Nafion® polymer can also be used as acatalyst. After addition of catalyst, reaction proceeds up to 30minutes. Viscous homogeneous polymer solution is formed at this stage.After the specified reaction time, the content of the high pressurevessel is transferred to a bath containing methanol, water and base,like ammonium hydroxide or sodium hydroxide to shortstop the reaction.After the solution is sufficiently quenched, the solution isprecipitated in deionized water. Fluffy granules of polymer are formed.Polymer granules are then centrifuged and vacuum dried. This polymer issoluble in, methanol, ethanol, propanol, butanol and their mixtures withwater of varying proportion. They are also soluble in blends ofdifferent alcohols.

[0112] Thus formed alkoxy alkyl modified type 8 polyamide is dissolvedin ethanol/water mixture. Polymer solution is electrospun in a mannerdescribed in Barris U.S. Pat. No. 4,650,516. Polymer solution viscositytends to increase with time. It is generally known that polymerviscosity has a great influence in determining fiber sizes. Thus, it isdifficult to control the process in commercial scale, continuousproduction. Furthermore, under same conditions, type 8 polyamides do notform microfibers as efficiently as copolyamides. However, when thesolution is prepared with addition of acidic catalyst, such as toluenesulfonic acid, maleic anhydride, trifluoro methane sulfonic acid, citricacid, ascorbic acid and the like, and fiber mats are carefullyheat-treated after fiber formation, the resultant fiber has a very goodchemical resistance. (FIG. 13). Care must be taken during thecrosslinking stage, so that one does not destroy fibrous structure.

[0113] We have found a surprising result when type 8 polyamide (polymerB) is blended with alcohol soluble copolyamides. By replacing 30% byweight of alkoxy alkyl modified polyamide 66 with alcohol solublecopolyamide like SVP 637 or 651 (polymer A), Elvamide 8061, synergisticeffects were found. Fiber formation of the blend is more efficient thaneither of the components alone. Soaking in ethanol and measuringfiltration efficiency shows better than 98% filtration efficiencyretention, THC bench testing showing comparable results with Type 8polyamide alone. This type blend shows that we can obtain advantage ofefficient fiber formation and excellent filtration characteristic ofcopolyamide with advantage of excellent chemical resistance ofcrosslinked type 8 polyamide. Alcohol soak test strongly suggests thatnon-crosslinkable copolyamide has participated in crosslinking tomaintain 98% of filtration efficiency.

[0114] DSC (see FIGS. 17-20) of blends of polymer A and B becomeindistinguishable from that of polymer A alone after they are heated to250 C°. (fully crosslinked) with no distinct melt temperature. Thisstrongly suggests that blends of polymer A and B are a fully integratedpolymer by polymer B crosslinking with polymer A. This is a completelynew class of polyamide.

[0115] Similarly, melt-blend poly (ethylene terephthalate) withpoly(butylene terephthalate) can have similar properties. During themelt processing at temperatures higher than melt temperature of eithercomponent, ester group exchange occurs and inter polymer of PET and PBTformed. Furthermore, our crosslinking temperature is lower than eitherof single component. One would not have expected that such groupexchange occur at this low temperature. Therefore, we believe that wefound a new family of polyamide through solution blending of Type A andType B polyamide and crosslinking at temperature lower than the meltingpoint of either component.

[0116] When we added 10% by weight of t-butyl phenol oligomer (Additive7) and heat treated at temperature necessary for crosslinkingtemperature, we have found even better results. We theorized thathydroxyl functional group of t-butyl phenol oligomers would participatein reaction with functional group of type 8 nylons. What we have foundis this component system provides good fiber formation, improvedresistance to high temperature and high humidity and hydrophobicity tothe surface of fine fiber layers.

[0117] We have prepared samples of mixture of Polymer A and Polymer B(Sample 6A) and another sample of mixture of Polymer A, Polymer B andAdditive & (Sample 6B). We then formed fiber by electrospinning process,exposed the fiber mat at 300° F. for 10 minutes and evaluated thesurface composition by ESCA surface analysis. TABLE 3 ESCA analysis ofSamples 6A and 6B. Composition (%) Sample 6A Sample 6B Polymer A 30 30Polymer B 70 70 Additive 7  0 10 Surface Composition W/O Heat W/Heat W/OHeat W/Heat Polymer A&B (%) 100 100 68.9 43.0 Additive 7  0  0 31.1 57.0

[0118] ESCA provides information regarding surface composition, exceptthe concentration of hydrogen. It provides information on carbon,nitrogen and oxygen. Since the Additive 7 does not contain nitrogen, wecan estimate the ratio of nitrogen containing polyamides and additivethat does not contain nitrogen by comparing concentration of nitrogen.Additional qualitative information is available by examining O 1 sspectrum of binding energy between 535 and 527 eV. C═O bond has abinding energy at around 531 eV and C—O bond has a binding energy at 533eV. By comparing peak heights at these two peaks, one can estimaterelative concentration of polyamide with predominant C═O and additivewith solely C—O groups. Polymer B has C—O linkage due to modificationand upon crosslinking the concentration of C—O will decrease. ESCAconfirms such reaction had indeed occurred, showing relative decrease ofC—O linkage. (FIG. 4 for non heat treated mixture fiber of Polymer A andPolymer B, FIG. 5 for heat treated mixture fiber of Polymer A andPolymer B). When Additive 7 molecules are present on the surface, onecan expect more of C—O linkage. This is indeed the case as can be seenin FIGS. 6 and 7. (FIG. 6 for as-spun mixture fibers of Polymer A,Polymer B and Additive 7. FIG. 7 for heat treated mixture fibers ofPolymer A, Polymer B and Additive 7). FIG. 6 shows that theconcentration of C—O linkage increases for Example 7. The finding isconsistent with the surface concentration based on XPS multiplexspectrum of FIGS. 8 through 11.

[0119] It is apparent that t-butyl oligomer molecules migrated towardthe surface of the fine fibers and form hydrophobic coating of about 50Å. Type 8 nylon has functional groups such as —CH₂OH and —CH₂OCH₃, whichwe expected to react with —OH group of t-butyl phenol. Thus, we expectedto see less oligomer molecules on the surface of the fibers. We havefound that our hypothesis was not correct and we found the surface ofthe interpolymer has a thin coating.

[0120] Samples 6A, 6B and a repeat of sample described in Section 5 havebeen exposed THC bench at 160° F. at 100% RH. In previous section, thesamples were exposed to 140° F. and 100% RH. Under these conditions,t-butyl phenol protected terpolymer copolyamide from degradation.However, if the temperature is raised to 160° F. and 100% RH, then thet-butyl phenol oligomer is not as good in protecting the underlyingterpolymer copolyamide fibers. We have compared samples at 160° F. and100% RH. TABLE 4 Retained Fine Fiber Efficiency after Exposure to 160°F. and 100% RH Sample After 1 Hr. After 2 Hrs. After 3 Hrs. Sample 6A82.6 82.6 85.9 Sample 6B 82.4 88.4 91.6 Sample 5 10.1

[0121] The table shows that Sample 6B helps protect exposure to hightemperature and high humidity.

[0122] More striking difference shows when we exposed to droplets ofwater on a fiber mat. When we place a drop of DI water in the surface ofSample 6A, the water drops immediately spread across the fiber mat andthey wet the substrate paper as well. On the other hand, when we place adrop of water on the surface of Sample 6B, the water drop forms a beadand did not spread on the surface of the mat. We have modified thesurface of Sample 16 to be hydrophobic by addition of oligomers ofp-t-butyl phenol. This type of product can be used as a water misteliminator, as water drops will not go through the fine fiber surfacelayer of Sample 6B.

[0123] Samples 6A, 6B and a repeat sample of Section 5 were placed in anoven where the temperature was set at 310° F. Table shows that bothSamples 6A and 6B remain intact while Sample of Section 5 was severelydamaged. TABLE 5 Retained Fine Fiber Efficiency after Exposure to 310°F. Sample After 6 Hrs. After 77 Hrs. Sample 6A 100% 100% Sample 6B 100%100% Sample 5  34%  33%

[0124] While addition of oligomer to Polymer A alone improved the hightemperature resistance of fine fiber layer, the addition of Additive 7has a neutral effect on the high temperature exposure.

[0125] We have clearly shown that the mixture of terpolymer copolyamide,alkoxy alkyl modified nylon 66 and oligomers of t-butyl phenol providesa superior products in helping fine fibers under severe environment withimproved productivity in manufacturing over either mixture of terpolymercopolyamide and t-butyl phenol oligomer or the mixture of terpolymercopolyamide and alkoxy alkyl modified nylon 66. These two componentsmixture are also improvement over single component system.

Example 7 Compatible Blend of Polyamides and Bisphenol a Polymers

[0126] A new family of polymers can be prepared by oxidative coupling ofphenolic ring (Pecora, A; Cyrus, W. U.S. Pat. No. 4,900,671(1990) andPecora, A; Cyrus, W.; Johnson, M. U.S. Pat. No. 5,153,298(1992)). Ofparticular interest is polymer made of Bisphenol A sold by Enzymol Corp.Soybean Peroxidase catalyzed oxidation of Bisphendl A can start fromeither side of two —OH groups in Bisphenol A. Unlike Bisphenol A basedpolycarbonate, which is linear, this type of Bisphenol A polymer formshyperbranched polymers. Because of hyperbranched nature of this polymer,they can lower viscosity of polymer blend.

[0127] We have found that this type of Bisphenol A polymer can besolution blended with polyamides. Reported Hansen's solubility parameterfor nylon is 18.6. (Page 317, Handbook of Solubility Parameters andother cohesion parameters, A. Barton ed., CRC Press, Boca Raton Fla.,1985) If one calculates solubility parameter (page 61, Handbook ofSolubility Parameters), then the calculated solubility parameter is28.0. Due to the differences in solubility parameter, one would notexpect that they would be miscible with each other. However, we foundthat they are quite miscible and provide unexpected properties.

[0128] 50:50 blend of Bisphenol A resin of M.W. 3,000 and copolyamidewas made in ethanol solution. Total concentration in solution was 10%.Copolyamide alone would have resulted in 0.2 micron fiber diameter.Blend resulted in lofty layer of fibers around 1 micron. Bisphenol A of7,000 M.W. is not stable with copolyamide and tends to precipitate.

[0129] DSC of 50:50 blend shows lack of melting temperature. Copolyamidehas melting temperature around 150 degree C. and Bisphenol A resin is aglassy polymer with Tg of about 100. The blend shows lack of distinctmelting. When the fiber mat is exposed to 100 degree C., the fiber matdisappears. This blend would make an excellent filter media where upperuse temperature is not very high, but low-pressure drop is required.This polymer system could not be crosslinked with a reasonable manner.

Example 8 Dual Roles of Bisphenol a Polymer as Solvent and Solid inBlend

[0130] A surprising feature of Bisphenol A polymer blend is that insolution form Bisphenol A polymer acts like a solvent and in solid formthe polymer acts as a solid. We find dual role of Bisphenol A polymertruly unique.

[0131] The following formulation is made: Alkoxy alkyl modified PA 66:Polymer B  180 g Bisphenol A Resin (3,000 MW): Polymer C  108 g Ethanol190 Grade  827 g Acetone  218 g DI water  167 g Catalyst  9.3 g

[0132] The viscosity of this blend was 32.6 centipoise by Brookfieldviscometer. Total polymer concentration was be 19.2%. Viscosity ofPolymer B at 19.2% is over 200 centipoise. Viscosity of 12% polymer Balone in similar solvent is around 60 centipoise. This is a clearexample that Bisphenol A resin acts like a solvent because the viscosityof the total solution was lower than expected. Resultant fiber diameterwas 0.157 micron. If polymer B alone participated in fiber formation,the expected fiber size would be less than 0.1 micron. In other words,Polymer C participated in fiber formation. We do not know of any othercase of such dramatic dual role of a component. After soaking the samplein ethanol, the filtration efficiency and fiber size was measured. Afteralcohol soak, 85.6% of filtration efficiency was retained and the fibersize was unchanged. This indicates that Polymer C has participated incrosslinking acting like a polymer solid.

[0133] Another polymer solution was prepared in the following manner:Alkoxy alkyl Modified PA66: Polymer B  225 g Bisphenol A Resin (3,000MW): Polymer C  135 g Ethanol 190 Grade  778 g Acetone  205 g DI Water 157 g Catalyst 11.6 g

[0134] Viscosity of this blend was 90.2 centipoise. This is a very lowviscosity value for 24% solid. Again, this is an indication Polymer Cacts like a solvent in the solution. However, when they are electrospuninto fiber, the fiber diameter is 0.438 micron. 15% solution of PolymerB alone would have produced around 0.2-micron fibers. In final state,Polymer C contributes to enlarging fiber sizes. Again, this exampleillustrates that this type of branched polymer acts as a solvent insolution and acts as a solid in final state. After soaking in ethanolsolution, 77.9% of filtration efficiency was retained and fiber size wasunchanged.

Example 9 Development of Crosslinked Polyamides/Bisphenol a PolymerBlends

[0135] Three different samples were prepared by combining resins,alcohols and water, stirring 2 hours at 60 degree C. The solution iscooled to room temperature and catalyst was added to solution and themixture was stirred another 15 minutes. Afterward, viscosity of solutionwas measured and spun into fibers.

[0136] The following table shows these examples: Recipe (g) Sample 9ASample 9B Sample 9C Polymer B 8.4 12.6 14.7 Polymer A 3.6 5.4 6.3Polymer C 7.2 10.8 12.6 Ethanol 190 Grade 89.3 82.7 79.5 Isopropanol23.5 21.8 21.0 DI Water 18.0 16.7 15.9 Catalyst .45 0.58 0.79 Viscosity(cP) 22.5 73.5 134.2 Fiber Size (micron) 0.14 0.258 0.496

[0137] We have found out that this blend generates fibers efficiently,producing about 50% more mass of fiber compared to Polymer A recipe. Inaddition, resultant polymeric microfibers produce a more chemicallyresistant fiber. After alcohol soak, a filter made from these fibersmaintained more than 90% filtration efficiency and unchanged fiberdiameter even though inherently crosslinkable polymer is only 44% of thesolid composition. This three-polymer composition of co-polyamide,alkoxy alkyl modified Nylon 66 and Bisphenol A creates excellent fiberforming, chemically resistant material.

Example 10 Alkoxy Alkyl Modified Co-Polymer of Nylon 66 and Nylon 46

[0138] In a 10-gallon high-pressure reactor, the following reactionswere made, and resultant polymers were analyzed. After reactiontemperature was reached, catalyst were added and reacted for 15 minutes.Afterward, the polymer solution was quenched, precipitated, washed anddried. Reactor Charge (LB) Run 10A Run 10B Run 10C Run 10D Run 10E Nylon4,6 (duPontZytel 101) 10 5 5 5 5 Nylon 6,6 (DSM Stanyl 300) 0 5 5 5 5Formaldehyde 8 10 8 10 8 DI Water 0.2 0.2 2 0.2 2 Methanol 22 20 20 2020 Reaction Temp (° C.) 140 140 140 150 150 Tg (° C.) 56.7 38.8 37.738.5 31.8 Tm (° C.) 241.1 162.3 184.9 175.4 189.5 Level of SubstitutionAlkoxy (wt. %) 11.9 11.7 7.1 11.1 8.4 Methylol (wt %) 0.14 0.13 0.140.26 0.24

[0139] DSC of the polymer made with Nylon 46 and Nylon 66 shows broadsingle melt temperature, which are lower than the melting temperature ofmodified Nylon 46 (241 C°) or modified Nylon 66 (210 C°). This is anindication that during the reaction, both components are randomlydistributed along the polymer chain. Thus, we believe that we haveachieved random copolymer of Nylon 46 and Nylon 66 with alkoxy alkylmodification. These polymers are soluble in alcohols and mixtures ofalcohol and water. Property ASTM Nylon 6.6 Nylon 4.6 T_(m) 265° C. 295°C. Tensile Strength D638 13.700 8.500 Elongation at Break D638 15-80 60Tensile Yield Strength D638   8000-12,000 Flexural Strength D790 17,800011,500 Tensile Modulus × 10³ psi D638 230-550 250 Izod Impact ft-lb/inof notch D256A 0.55-1.0  17 Deflection Temp Under D648 158 194 FlexuralLoad 264 psi

[0140] Both are highly crystalline and are not soluble in commonalcohols.

[0141] Source: Modern Plastics Encyclopedia 1998

Example 11 Development of Interpolymer of Copolyamides and AlkoxyalkylModified Nylon 46/66 Copolymer and Formation of Electrospun Fibers

[0142] Runs 10B and 10D samples were made into fibers by methodsdescribed in above. Alkoxy alkyl modified Nylon 46/66 (Polymer D) alonewere successfully electrospun. Blending Polymer D with Polymer A bringsadditional benefits of more efficient fiber formation and ability tomake bigger fibers without sacrificing the crosslinkability of Polymer Das can be seen in the following table: Polymer 10B Polymer 10D w/30%w/30% Alone Polymer A Alone Polymer A Fiber Size(micron) 0.183 0.4640.19 0.3 Fiber Mass Ratio 1 3 1 2 Filtration Effi. 87 90 92 90Retention(%)

[0143] Fiber Mass Ratio is calculated by (total length of fiber timescross sectional area). Filtration Efficiency Retention is measuredsoaking filter sample in ethanol. Fiber size was unchanged by alcoholsoak.

Example 12 Crosslinked, Electrospun PVA

[0144] PVA powders were purchased from Aldrich Chemicals. They weredissolved either in water or 50/50 mixture of methanol and water. Theywere mixed with crosslinking agent and toluene sulfonic acid catalystbefore electrospinning. The resulting fiber mat was crosslinked in anoven at 150° C. for 10 minutes before exposing to THC bench. Sample 12ASample 12B Sample 12C Sample 12D PVA Hydrolysis 98-99 87-89 87-89 87-89M.W. 31,500-50,000 31,500-50,000 31,500-50,000 31,500-50,000 PVA Conc.(%) 10 10 10 10 Solvent Water Mixture Mixture (c) Mixture (d) OtherPolymer None None Acrylic Acid Cymel 385 Other Polymer/  0  0 30 30 PVA(%) % Fiber 0 (a) 0 (a,b) 95 (b) 20 (b) Retained THC, 1 hr. % Fiber 90(a) Retained THC, 3 hr.

Example 13

[0145] A conventional cellulose air filter media was used as thesubstrate. This substrate had a basis weight of 67 pounds per 3000square feet, a Frazier permeability of 16 feet per minute at 0.5 inchesof water pressure drop, a thickness of 0.012 inches, and a LEFSefficiency of 41.6%. A fine fiber layer of Example 1 was added to thesurface using the process described with a nominal fiber diameter of 0.2microns. The resulting composite had a LEFS efficiency of 63.7%. Afterexposure to 140 F air at 100% relative humidity for 1 hour the substrateonly sample was allowed to cool and dry, it then had a LEFS efficiencyof 36.5%. After exposure to 140 F air at 100% relative humidity for 1hour the composite sample was allowed to cool and dry, it then had aLEFS efficiency of 39.7%. Using the mathematical formulas described, thefine fiber layer efficiency retained after 1 hour of exposure was 13%,the number of effective fine fibers retained was 11%.

Example 14

[0146] A conventional cellulose air filter media was used as thesubstrate. This substrate had a basis weight of 67 pounds per 3000square feet, a Frazier permeability of 16 feet per minute at 0.5 inchesof water pressure drop, a thickness of 0.012 inches, and a LEFSefficiency of 41.6%. A fine fiber layer of Example 5 was added to thesurface using the process described with a nominal fiber diameter of 0.2microns. The resulting composite had a LEFS efficiency of 96.0%. Afterexposure to 160 F air at 100% relative humidity for 3 hours thesubstrate only sample was allowed to cool and dry, it then had a LEFSefficiency of 35.3%. After exposure to 160 F air at 100% relativehumidity for 3 hours the composite sample was allowed to cool and dry,it then had a LEFS efficiency of 68.0%. Using the mathematical formulasdescribed, the fine fiber layer efficiency retained after 3 hours ofexposure was 58%, the number of effective fine fibers retained was 29%.

Example 15

[0147] A conventional cellulose air filter media was used as thesubstrate. This substrate had a basis weight of 67 pounds per 3000square feet, a Frazier permeability of 16 feet per minute at 0.5 inchesof water pressure drop, a thickness of 0.012 inches, and a LEFSefficiency of 41.6%. A fine fiber layer of a blend of Polymer A andPolymer B as described in Example 6 was added to the surface using theprocess described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 92.9%. After exposure to160 F air at 100% relative humidity for 3 hours the substrate onlysample was allowed to cool and dry, it then had a LEFS efficiency of35.3%. After exposure to 160 F air at 100% relative humidity for 3 hoursthe composite sample was allowed to cool and dry, it then had a LEFSefficiency of 86.0%. Using the mathematical formulas described, the finefiber layer efficiency retained after 3 hours of exposure was 96%, thenumber of effective fine fibers retained was 89%.

Example 16

[0148] A conventional cellulose air filter media was used as thesubstrate. This substrate had a basis weight of 67 pounds per 3000square feet, a Frazier permeability of 16 feet per minute at 0.5 inchesof water pressure drop, a thickness of 0.012 inches, and a LEFSefficiency of 41.6%. A fine fiber layer of Polymer A, Polymer B, t-butylphenol oligomer as described in Example 6 was added to the surface usingthe process described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 90.4%. After exposure to160 F air at 100% relative humidity for 3 hours the substrate onlysample was allowed to cool and dry, it then had a LEFS efficiency of35.3%. After exposure to 160 F air at 100% relative humidity for 3 hoursthe composite sample was allowed to cool and dry, it then had a LEFSefficiency of 87.3%. Using the mathematical formulas described, the finefiber layer efficiency retained after 3 hours of exposure was 97%, thenumber of effective fine fibers retained was 92%.

Example 17

[0149] A conventional cellulose air filter media was used as thesubstrate. This substrate had a basis weight of 67 pounds per 3000square feet, a Frazier permeability of 16 feet per minute at 0.5 inchesof water pressure drop, a thickness of 0.012 inches, and a LEFSefficiency of 41.6%. A fine fiber layer of crosslinked PVA withpolyacrylic acid of Example 12 was added to the surface using theprocess described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 92.9%. After exposure to160 F air at 100% relative humidity for 2 hours the substrate onlysample was allowed to cool and dry, it then had a LEFS efficiency of35.3%. After exposure to 160 F air at 100% relative humidity for 2 hoursthe composite sample was allowed to cool and dry, it then had a LEFSefficiency of 83.1%. Using the mathematical formulas described, the finefiber layer efficiency retained after 2 hours of exposure was 89%, thenumber of effective fine fibers retained was 76%.

Example 18

[0150] The following filter medias have been made with the methodsdescribed in Example 1-17. Filter Media Examples Substrate permSubstrate Basis wt Substrate Substrate Composite Substrate (Frazier)(lbs/3000 sq ft) Thickness (in) Eff (LEFS) Eff (LEFS Single fine fiberlayer on (+/−10% (+/−10%) (+/−25%) (+/−5%) (+/−5%) single substrate(flow either direction through media Cellulose air filter media 58 670.012 11% 50% Cellulose air filter media 16 67 0.012 43% 58% Celluloseair filter media 58 67 0.012 11% 65% Cellulose air filter media 16 670.012 43% 70% Cellulose air filter media 22 52 0.010 17% 70% Celluloseair filter media 16 67 0.012 43% 72% Cellulose/synthetic blend 14 700.012 30% 70% with moisture resistant resin Flame retardant cellulose 1777 0.012 31% 58% air filter media Flame retardant cellulose 17 77 0.01231% 72% air filter media Flame retardant synthetic 27 83 0.012 77% airfilter media Spunbond Remay 1200 15 0.007  5% 55% (polyester)Synthetic/cellulose air 260 76 0.015  6% 17% filter mediaSynthetic/glass air filter 31 70 0.012 55% 77% media Synthetic/glass airfilter 31 70 0.012 50% 90% media Synthetic (Lutrador- 300 25 0.008  3%65% polyester) Synthetic (Lutrador- 0.016 90% polyester)

[0151] Media has been used flat, corrugated, pleated, corrugated andpleated, in flatsheets, pleated flat panels, pleated round filters, andZee filters.

Test Methods

[0152] Hot Water Soak Test

[0153] Using filtration efficiency as the measure of the number of finefibers effectively and functionally retained in structure has a numberof advantages over other possible methods such as SEM evaluation.

[0154] the filtration measure evaluates several square inches of mediayielding a better average than the tiny area seen in SEMphotomicrographs (usually less than 0.0001 square inch

[0155] the filtration measurement quantifies the number of fibersremaining functional in the structure. Those fibers that remain, but areclumped together or otherwise existing in an altered structure are onlyincluded by their measured effectiveness and functionality.

[0156] Nevertheless, in fibrous structures where the filtrationefficiency is not easily measured, other methods can be used to measurethe percent of fiber remaining and evaluated against the 50% retentioncriteria.

[0157] Description: This test is an accelerated indicator of filtermedia moisture resistance. The test uses the LEFS test bench to measurefilter media performance changes upon immersion in water. Watertemperature is a critical parameter and is chosen based on thesurvivability history of the media under investigation, the desire tominimize the test time and the ability of the test to discriminatebetween media types. Typical water temperatures re 70° F., 140° F. or160° F.

[0158] Procedure:

[0159] A 4″ diameter sample is cut from the media. Particle captureefficiency of the test specimen is calculated using 0.8 μm latex spheresas a test challenge contaminant in the LEFS (for a description of theLEFS test, see ASTM Standard F1215-89) bench operating at 20 FPM. Thesample is then submerged in (typically 140° F.) distilled water for 5minutes. The sample is then placed on a drying rack and dried at roomtemperature (typically overnight). Once it is dry the sample is thenretested for efficiency on the LEFS bench using the same conditions forthe initial calculation.

[0160] The previous steps are repeated for the fine fiber supportingsubstrate without fine fiber.

[0161] From the above information one can calculate the efficiencycomponent due only to the fine fiber and the resulting loss inefficiency due to water damage. Once the loss in efficiency due to thefine fiber is determined one can calculate the amount of efficiencyretained.

[0162] Calculations:

[0163] Fine fiber layer efficiency: E_(i)=Initial Composite Efficiency;

[0164] E_(s)=Initial Substrate Efficiency;

[0165] F_(e)=Fine Fiber Layer

[0166] F_(e)=1−EXP(Ln(1−E_(i))−Ln(1−E_(x)))

[0167] Fine fiber layer efficiency retained: F_(i)=Initial fine fiberlayer efficiency;

[0168] F_(x)=Post soak fine fiber layer efficiency;

[0169] F_(r)=Fine fiber retained

F _(r) =F _(x) /F _(i)

[0170] The percentage of the fine fibers retained with effectivefunctionality can also be calculated by:

%=log(1−F_(x))/log(1−F_(i))

[0171] Pass/Fail Criteria: >50% efficiency retention

[0172] In most industrial pulse cleaning filter applications the filterwould perform adequately if at least 50% of the fine fiber efficiency isretained.

[0173] THC Bench (Temperature, Humidity

[0174] Description: The purpose of this bench is to evaluate fine fibermedia resistance to the affects of elevated temperature and highhumidity under dynamic flow conditions. The test is intended to simulateextreme operating conditions of either an industrial filtrationapplication, gas turbine inlet application, or heavy duty engine airintake environments. Samples are taken out, dried and LEFS tested atintervals. This system is mostly used to simulate hot humid conditionsbut can also be used to simulate hot/cold dry situations. Temperature−31 to 390° F. Humidity    0 to 100% RH (Max temp for 100% RH is 160° F.and max continuous duration at this condition is 16 hours) Flow Rate   1 to 35 FPM

[0175] Procedure:

[0176] A 4″ diameter sample is cut from the media.

[0177] Particle capture efficiency of the test specimen is calculatedusing 0.8 μm latex spheres as a test challenge contaminant in the LEFSbench operating at 20 FPM.

[0178] The sample is then inserted into the THC media chuck.

[0179] Test times can be from minutes to days depending on testingconditions.

[0180] The sample is then placed on a drying rack and dried at roomtemperature (typically overnight). Once it is dry the sample is thenretested for efficiency on the LEFS bench using the same conditions forthe initial calculation.

[0181] The previous steps are repeated for the fine fiber supportingsubstrate without fine fiber. From the above information one cancalculate the efficiency component due only to the fine fiber and theresulting loss in efficiency due to alcohol damage.

[0182] Once the loss in efficiency due to the fine fiber is determinedone can calculate the amount of efficiency retained.

[0183] Pass/Fail Criteria: >50% efficiency retention

[0184] In most industrial pulse cleaning filter applications the filterwould perform adequately if at least 50% of the fine fiber efficiency isretained.

[0185] Alcohol (Ethanol) Soak Test

[0186] Description: The test uses the LEFS test bench to measure filtermedia performance changes upon immersion in room temperature ethanol.

[0187] Procedure:

[0188] A 4″ diameter sample is cut from the media. Particle captureefficiency of the test specimen is calculated using 0.8 μm latex spheresas a test challenge contaminant in the LEFS bench operating at 20 FPM.The sample is then submerged in alcohol for 1 minute.

[0189] The sample is then placed on a drying rack and dried at roomtemperature (typically overnight). Once it is dry the sample is thenretested for efficiency on the LEFS bench using the same conditions forthe initial calculation. The previous steps are repeated for the finefiber supporting substrate without fine fiber. From the aboveinformation one can calculate the efficiency component due only to thefine fiber and the resulting loss in efficiency due to alcohol damage.Once the loss in efficiency due to the fine fiber is determined one cancalculate the amount of efficiency retained.

[0190] Pass/Fail Criteria: >50% efficiency retention.

[0191] The above specification, examples and data provide an explanationof the invention. However, many variations and embodiments can be madeto the disclosed invention. The invention is embodied in the claimsherein after appended.

1. A filter structure for filtering air in a gas turbine intake system,the turbine operating at an intake air demand greater than 8000ft³-min⁻¹, the intake air having an ambient temperature and a humidityof at least 50% RH, the structure comprising, in an air intake of a gasturbine system, at least one filter element, the filter element having amedia pack forming a tubular construction and construction defining aopen filter interior; the open filter interior being a clean air plenum,the media pack including a pleated construction of a media composite,the media composite including a substrate at least partially covered bya layer of fine fibers, the fine fibers comprising a polymericcomposition comprising an addition polymer or a condensation polymerother than a copolymer formed from a cyclic lactam and a C₆₋₁₀ diaminemonomer or a C₆₋₁₀ diacid monomer combined with an additive material. 2.The structure of claim 1 wherein the substrate comprises a cellulosicfiber, a synthetic fiber or mixtures thereof.
 3. The structure of claim1 wherein the additive comprises an oligomer having a molecular weightof about 500 to 3000 and an aromatic character free of an alkyl moietywherein the additive is miscible in the condensation polymer; andcomprising the step of directing the air through the media pack of thefilter element and into the open filter interior to clean the air. 4.The structure of claim 1 wherein the polymer comprises a polyalkyleneterephthalate.
 5. The structure of claim 1 wherein the polymer comprisesa polyalkylene naphthalate.
 6. The structure of claim 1 wherein thepolymer comprises a polyethylene terephthalate.
 7. The structure ofclaim 1 wherein the polymer comprises a nylon polymer.
 8. The structureof claim 7 wherein the nylon copolymer is combined with a second nylonpolymer, the second nylon polymer differing in molecular weight ormonomer.
 9. The structure of claim 8 wherein the nylon copolymer iscombined with a second nylon polymer, the second nylon polymercomprising an alkoxy alkyl modified polyamide.
 10. The structure ofclaim 8 wherein the second nylon polymer comprises a nylon copolymer.11. The structure of claim 8 wherein the polymers are treated to form asingle polymeric composition as measured by a differential scanningcalorimeter showing a single-phase material.
 12. The structure of claim11 wherein the copolymer and the second polymer are heat-treated. 13.The structure of claim 12 wherein the copolymer and the second polymerare heat-treated to a temperature less than the lower melting point ofthe polymers.
 14. The structure of claim 1 wherein the additivecomprises an oligomer comprising tertiary butyl phenol.
 15. Thestructure of claim 14 wherein the additive comprises an oligomercomprising:


16. The structure of claim 1 wherein the resin comprises an oligomercomprising bis-phenol A.
 17. The structure of claim 16 wherein theadditive comprises an oligomer comprising:


18. The structure of claim 1 wherein the additive comprises an oligomercomprising dihydroxy biphenyl.
 19. The structure of claim 18 wherein theadditive comprises an oligomer comprising:


20. The structure of claim 1 wherein the additive comprises a blend ofthe resinous additive and a fluoropolymer.
 21. The structure of claim 1wherein the additive comprises a fluorocarbon surfactant.
 22. Thestructure of claim 1 wherein the additive comprises a nonionicsurfactant.
 23. The structure of claim 1 wherein the condensationpolymer comprises a polyurethane polymer.
 24. The structure of claim 1wherein the condensation polymer comprises a blend of a polyurethanepolymer and a polyamide polymer.
 25. The structure of claim 24 whereinthe polyamide polymer comprises a nylon.
 26. The structure of claim 25wherein the nylon comprises a nylon homopolymer, a nylon copolymer ormixtures thereof.
 27. The structure of claim 1 wherein the condensationpolymer comprises an aromatic polyamide.
 28. The structure of claim 1wherein the condensation polymer comprises a reaction product of adiamine monomer and poly(m-phenylene isophthalamide).
 29. The structureof claim 28 wherein the polyamide comprises a reaction product of adiamine and a poly(p-phenylene terephthalamide).
 30. The structure ofclaim 1 wherein the condensation polymer comprises a polybenzimidazole.31. The structure of claim 1 wherein the condensation polymer comprisesa polyarylate.
 32. The structure of claim 31 wherein the polyarylatepolymer comprises a condensation polymerization reaction product betweenbis-phenol-A and mixed phthalic acids.
 33. A method for filtering air ina gas turbine intake system, the turbine operating at an air intakedemand of at least 8000 ft³-min⁻¹, the intake air having an ambienttemperature and a humidity of at least 50% RH, the method comprising thesteps of: (a) installing a filter proximate an air intake of a gasturbine system, the filter comprising at least one filter element, thefilter element having a media pack forming a tubular construction andconstruction defining a open filter interior; the open filter interiorbeing a clean air plenum, the media pack including a pleatedconstruction of a media composite, the media composite including asubstrate at least partially covered by a layer of fine fibers, the finefibers comprising a polymeric composition comprising an addition polymeror a condensation polymer other than a copolymer formed from a cycliclactam and a C₆₋₁₀ diamine monomer or a C₆₋₁₀ diacid monomer combinedwith an additive material; and (b) directing intake air into an airintake of a gas turbine system
 34. The method of claim 33 wherein theadditive comprises an oligomer having a molecular weight of about 500 to3000 and an aromatic character free of an alkyl phenolic moiety whereinthe additive is miscible in the condensation polymer; and comprising thestep of directing the air through the media pack of the filter elementand into the open filter interior to clean the air.
 35. The compositionof claim 33 wherein the polymer comprises a polyalkylene terephthalate.36. The composition of claim 33 wherein the polymer comprises apolyalkylene naphthalate.
 37. The composition of claim 33 wherein thepolymer comprises a polyethylene terephthalate.
 38. The composition ofclaim 33 wherein the polymer comprises a nylon polymer.
 39. Thecomposition of claim 33 wherein the nylon copolymer is combined with asecond nylon polymer, the second nylon polymer differing in molecularweight or monomer composition.
 40. The composition of claim 33 whereinthe nylon copolymer is combined with a second nylon polymer, the secondnylon polymer comprising an alkoxy alkyl modified polyamide.
 41. Thecomposition of claim 39 wherein the second nylon polymer comprises anylon copolymer.
 42. The composition of claim 39 wherein the polymersare treated to form a single polymeric composition as measured by adifferential scanning calorimeter showing a single-phase material. 43.The composition of claim 42 wherein the copolymer and the second polymerare heat-treated.
 44. The composition of claim 43 wherein the copolymerand the second polymer are heat-treated to a temperature less than thelower melting point of the polymers.
 45. The composition of claim 1wherein the additive comprises an oligomer comprising tertiary butylphenol.
 46. The composition of claim 45 wherein the additive comprisesan oligomer comprising:


47. The composition of claim 33 wherein the resin comprises an oligomercomprising bis-phenol A.
 48. The composition of claim 47 wherein theadditive comprises an oligomer comprising:


49. The composition of claim 33 wherein the resin comprises an oligomercomprising dihydroxy biphenyl.
 50. The composition of claim 49 whereinthe additive comprises an oligomer comprising:


51. The composition of claim 33 wherein the additive comprises a blendof the resinous additive and a fluoropolymer.
 52. The composition ofclaim 33 wherein the additive comprises a fluorocarbon surfactant. 53.The composition of claim 33 wherein the additive comprises a nonionicsurfactant.
 54. The composition of claim 33 wherein the condensationpolymer comprises a polyurethane polymer.
 55. The composition of claim33 wherein the condensation polymer comprises a blend of a polyurethanepolymer and a polyamide polymer.
 56. The composition of claim 55 whereinthe polyamide polymer comprises a nylon.
 57. The composition of claim 56wherein the nylon comprises a nylon homopolymer, a nylon copolymer ormixtures thereof.
 58. The composition of claim 33 wherein thecondensation polymer comprises an aromatic polyamide.
 59. Thecomposition of claim 33 wherein the condensation polymer comprises areaction product of a diamine monomer and poly(m-phenyleneisophthalamide).
 60. The composition of claim 58 wherein the polyamidecomprises a reaction product of a diamine and a poly(p-phenyleneterephthalamide).
 61. The composition of claim 33 wherein thecondensation polymer comprises a polybenzimidazole.
 62. The compositionof claim 33 wherein the condensation polymer comprises a polyarylate.63. The composition of claim 29 wherein the polyarylate polymercomprises a condensation polymerization reaction product betweenbis-phenol-A and mixed phthalic acids.
 64. The method according to claim33 wherein, said step of directing air into an air intake of a gasturbine system having at least one filter element includes directing airinto an air intake of a gas turbine system having a plurality of filterelement pairs, each of the filter element pairs including a firsttubular filter element with the media pack sealed against an end of asecond tubular filter element with the media pack; each of the first andsecond tubular filter elements defining the clean air plenum.
 65. Amethod according to claim 33 wherein said step of directing air into anair intake of a gas turbine system having a plurality of filter elementpairs includes directing air into the first tubular filter element andthe second tubular filter element; wherein the first tubular filterelement is cylindrical and the second tubular filter element is conical.66. A method according to claim 33 further including directing a pulseof air into each of the clean air plenums of each of the filter elementpairs to at least partially remove particulates collected on each of themedia packs.
 67. A method for filtering air in a gas turbine intakesystem, the method comprising, in a turbine operating at an air intakedemand greater than 8000 ft³-min⁻¹, an intake air having an ambienttemperature and a humidity of at least 50% RH, (a) directing intake airinto an air intake of a gas turbine system having at least one filterelement, the filter element having a media pack forming a tubularconstruction and construction defining a open filter interior; the openfilter interior being a clean air plenum, the media pack including apleated construction of a media composite, the media composite includinga substrate at least partially covered by a layer of fine fibers, thefine fibers comprising a condensation polymer, other than a copolymerformed from a cyclic lactam and a C₆₋₁₀ diamine monomer or a C₆₋₁₀diacid monomer, and a resinous additive comprising an oligomer having amolecular weight of about 500 to 3000 and an aromatic character whereinthe additive miscible in the condensation polymer; and (b) directing theair through the media pack of the filter element and into the openfilter interior to clean the air.
 68. The composition of claim 67wherein the condensation polymer comprises a polyalkylene terephthalate.69. The composition of claim 67 wherein the condensation polymercomprises a polyalkylene naphthalate.
 70. The composition of claim 67wherein the condensation polymer comprises a polyethylene terephthalate.71. The composition of claim 67 wherein the condensation polymercomprises a nylon polymer comprising a homopolymer having repeatingunits derived from a cyclic lactam.
 72. The composition of claim 67wherein the nylon copolymer is combined with a second nylon polymer, thesecond nylon polymer differing in molecular weight or monomercomposition.
 73. The composition of claim 67 wherein the nylon copolymeris combined with a second nylon polymer, the second nylon polymercomprising an alkoxy alkyl modified polyamide.
 74. The composition ofclaim 73 wherein the second nylon polymer comprises a nylon copolymer.75. The composition of claim 73 wherein the polymers are treated to forma single polymeric composition as measured by a differential scanningcalorimeter showing a single phase material.
 76. The composition ofclaim 74 wherein the copolymer and the second polymer are heat treated.77. The composition of claim 74 wherein the copolymer and the secondpolymer are heat treated to a temperature less than the lower meltingpoint of the polymers.
 78. The composition of claim 67 wherein theadditive comprises an oligomer comprising tertiary butyl phenol.
 79. Thecomposition of claim 78 wherein the additive comprises an oligomercomprising:


80. The composition of claim 67 wherein the resin comprises an oligomercomprising bis-phenol A.
 81. The composition of claim 80 wherein theadditive comprises an oligomer comprising:


82. The composition of claim 67 wherein the resin comprises an oligomercomprising dihydroxy biphenyl.
 83. The composition of claim 82 whereinthe additive comprises an oligomer comprising:


84. The composition of claim 67 wherein the additive comprises a blendof the resinous additive and a fluoropolymer.
 85. The composition ofclaim 67 wherein the additive comprises a fluorocarbon surfactant. 86.The composition of claim 67 wherein the additive comprises a nonionicsurfactant.
 87. The composition of claim 67 wherein the condensationpolymer comprises a polyurethane polymer.
 88. The composition of claim67 wherein the condensation polymer comprises a blend of a polyurethanepolymer and a polyamide polymer.
 89. The composition of claim 88 whereinthe polyamide polymer comprises a nylon.
 90. The composition of claim 89wherein the nylon comprises a nylon homopolymer, a nylon copolymer ormixtures thereof.
 91. The composition of claim 67 wherein thecondensation polymer comprises an aromatic polyamide.
 92. Thecomposition of claim 67 wherein the condensation polymer comprises areaction product of a diamine monomer and poly(m-phenyleneisophthalamide).
 93. The composition of claim 92 wherein the polyamidecomprises a reaction product of a diamine and a poly(p-phenyleneterephthalamide).
 94. The composition of claim 67 wherein thecondensation polymer comprises a polybenzimidazole.
 95. The compositionof claim 67 wherein the condensation polymer comprises a polyarylate.96. The composition of claim 29 wherein the polyarylate polymercomprises a condensation polymerization reaction product betweenbis-phenol-A and mixed phthalic acids.
 97. The method according to claim67 wherein, said step of directing air into an air intake of a gasturbine system having at least one filter element includes directing airinto an air intake of a gas turbine system having a plurality of filterelement pairs, each of the filter element pairs including a firsttubular filter element with the media pack sealed against an end of asecond tubular filter element with the media pack; each of the first andsecond tubular filter elements defining the clean air plenum.
 98. Amethod according to claim 67 wherein said step of directing air into anair intake of a gas turbine system having a plurality of filter elementpairs includes directing air into the first tubular filter element andthe second tubular filter element; wherein the first tubular filterelement is cylindrical and the second tubular filter element is conical.99. A method according to claim 67 further including directing a pulseof air into each of the clean air plenums of each of the filter elementpairs to at least partially remove particulates collected on each of themedia packs.